I didn't get another freeze yesterday when I tried using dwm instead of qtile. However I just got one immediately after sddm started again. This time I saved the output of dmesg and found some lines that might be related:
[ 9.698774] NVRM: GPU at PCI:0000:2b:00: GPU-5ad82855-a427-6810-21ce-41d8dacfae75
[ 9.698778] NVRM: Xid (PCI:0000:2b:00): 62, pid=2268, 21b5(3200) 00000000 00000000
[ 9.934829] NVRM: Xid (PCI:0000:2b:00): 13, pid=2268, Graphics Exception: Shader Program Header 1 Error
[ 9.934843] NVRM: Xid (PCI:0000:2b:00): 13, pid=2268, Graphics Exception: Shader Program Header 2 Error
[ 9.934854] NVRM: Xid (PCI:0000:2b:00): 13, pid=2268, Graphics Exception: Shader Program Header 9 Error
[ 9.934864] NVRM: Xid (PCI:0000:2b:00): 13, pid=2268, Graphics Exception: Shader Program Header 11 Error
[ 9.934874] NVRM: Xid (PCI:0000:2b:00): 13, pid=2268, Graphics Exception: ESR 0x405840=0xa0000a06
[ 9.934888] NVRM: Xid (PCI:0000:2b:00): 13, pid=2268, Graphics Exception: ESR 0x405848=0x80000000
[ 9.935221] NVRM: Xid (PCI:0000:2b:00): 13, pid=2279, Graphics Exception: ChID 0013, Class 0000c597, Offset 00000100, Data 00000000
[ 10.462104] NVRM: Xid (PCI:0000:2b:00): 31, pid=2189, Ch 00000009, intr 00000000. MMU Fault: ENGINE HOST0 HUBCLIENT_HOST faulted @ 0x1_0032f000. Fault is of type FAULT_PDE ACCESS_TYPE_VIRT_READ
[ 11.474770] NVRM: Xid (PCI:0000:2b:00): 31, pid=2189, Ch 00000009, intr 00000000. MMU Fault: ENGINE HOST0 HUBCLIENT_HOST faulted @ 0x1_0032f000. Fault is of type FAULT_PDE ACCESS_TYPE_VIRT_READ
[ 12.485803] NVRM: Xid (PCI:0000:2b:00): 31, pid=2189, Ch 00000009, intr 00000000. MMU Fault: ENGINE HOST0 HUBCLIENT_HOST faulted @ 0x1_0032f000. Fault is of type FAULT_PDE ACCESS_TYPE_VIRT_READ
[ 13.496695] NVRM: Xid (PCI:0000:2b:00): 31, pid=2189, Ch 00000009, intr 00000000. MMU Fault: ENGINE HOST0 HUBCLIENT_HOST faulted @ 0x1_0032f000. Fault is of type FAULT_PDE ACCESS_TYPE_VIRT_READ
[ 16.539884] NVRM: Xid (PCI:0000:2b:00): 45, pid=2189, Ch 00000000
[ 16.540399] NVRM: Xid (PCI:0000:2b:00): 45, pid=2189, Ch 00000001
[ 16.540819] NVRM: Xid (PCI:0000:2b:00): 45, pid=2189, Ch 00000008
[ 16.541228] NVRM: Xid (PCI:0000:2b:00): 45, pid=2189, Ch 00000009
[ 16.541626] NVRM: Xid (PCI:0000:2b:00): 45, pid=2279, Ch 00000010
[ 16.542028] NVRM: Xid (PCI:0000:2b:00): 45, pid=2279, Ch 00000011
[ 16.542426] NVRM: Xid (PCI:0000:2b:00): 45, pid=2279, Ch 00000012
[ 16.542825] NVRM: Xid (PCI:0000:2b:00): 45, pid=2279, Ch 00000016
[ 16.543228] NVRM: Xid (PCI:0000:2b:00): 45, pid=2279, Ch 00000017
[ 16.543626] NVRM: Xid (PCI:0000:2b:00): 45, pid=2279, Ch 00000018
[ 16.544028] NVRM: Xid (PCI:0000:2b:00): 45, pid=2279, Ch 00000019
[ 16.544426] NVRM: Xid (PCI:0000:2b:00): 45, pid=2279, Ch 0000001a
[ 16.544825] NVRM: Xid (PCI:0000:2b:00): 45, pid=2279, Ch 0000001b
[ 16.922957] random: crng init done
[ 16.922958] random: 3 urandom warning(s) missed due to ratelimiting
[ 17.234353] elogind[1417]: Removed session c1.
[ 17.280196] NVRM: Xid (PCI:0000:2b:00): 45, pid=2189, Ch 00000000
[ 17.280639] NVRM: Xid (PCI:0000:2b:00): 45, pid=2189, Ch 00000001
[ 17.281045] NVRM: Xid (PCI:0000:2b:00): 45, pid=2279, Ch 00000010
[ 17.281447] NVRM: Xid (PCI:0000:2b:00): 45, pid=2279, Ch 00000011
[ 17.281852] NVRM: Xid (PCI:0000:2b:00): 45, pid=2279, Ch 00000012
[ 17.282254] NVRM: Xid (PCI:0000:2b:00): 45, pid=2279, Ch 00000017
[ 17.282666] NVRM: Xid (PCI:0000:2b:00): 45, pid=2279, Ch 00000018
[ 17.283067] NVRM: Xid (PCI:0000:2b:00): 45, pid=2279, Ch 0000001a
[ 17.283472] NVRM: Xid (PCI:0000:2b:00): 45, pid=2279, Ch 0000001b
[ 17.293604] NVRM: Xid (PCI:0000:2b:00): 45, pid=2189, Ch 00000000
[ 17.294023] NVRM: Xid (PCI:0000:2b:00): 45, pid=2189, Ch 00000001
[ 26.386298] NVRM: GPU 0000:2b:00.0: RmInitAdapter failed! (0x23:0x65:1204)
[ 26.386330] NVRM: GPU 0000:2b:00.0: rm_init_adapter failed, device minor number 0
[ 30.391018] NVRM: GPU 0000:2b:00.0: RmInitAdapter failed! (0x23:0x65:1204)
[ 30.391049] NVRM: GPU 0000:2b:00.0: rm_init_adapter failed, device minor number 0
[ 36.514882] NVRM: GPU 0000:2b:00.0: RmInitAdapter failed! (0x23:0x65:1204)
[ 36.514909] NVRM: GPU 0000:2b:00.0: rm_init_adapter failed, device minor number 0
[ 40.519306] NVRM: GPU 0000:2b:00.0: RmInitAdapter failed! (0x23:0x65:1204)
[ 40.519337] NVRM: GPU 0000:2b:00.0: rm_init_adapter failed, device minor number 0
[ 43.841829] elogind[1417]: New session 3 of user myu.
[ 166.984991] NVRM: GPU 0000:2b:00.0: RmInitAdapter failed! (0x23:0x65:1204)
[ 166.985023] NVRM: GPU 0000:2b:00.0: rm_init_adapter failed, device minor number 0
[ 170.988104] NVRM: GPU 0000:2b:00.0: RmInitAdapter failed! (0x23:0x65:1204)
[ 170.988133] NVRM: GPU 0000:2b:00.0: rm_init_adapter failed, device minor number 0
[ 177.111425] NVRM: GPU 0000:2b:00.0: RmInitAdapter failed! (0x23:0x65:1204)
[ 177.111457] NVRM: GPU 0000:2b:00.0: rm_init_adapter failed, device minor number 0
[ 181.114456] NVRM: GPU 0000:2b:00.0: RmInitAdapter failed! (0x23:0x65:1204)
[ 181.114490] NVRM: GPU 0000:2b:00.0: rm_init_adapter failed, device minor number 0
[ 187.152510] NVRM: GPU 0000:2b:00.0: RmInitAdapter failed! (0x23:0x65:1204)
[ 187.152544] NVRM: GPU 0000:2b:00.0: rm_init_adapter failed, device minor number 0
[ 191.155570] NVRM: GPU 0000:2b:00.0: RmInitAdapter failed! (0x23:0x65:1204)
[ 191.155597] NVRM: GPU 0000:2b:00.0: rm_init_adapter failed, device minor number 0
"[ 43.841829] elogind[1417]: New session 3" was caused by me restarting sddm, which made the screens show nothing (besides visual glitches). Notably it seemed like the glitches were mirrored, but I'd have to look into that again the next time it happens. I also looked up "RmInitAdapter failed" but in hindsight it's probably just an error that occurred due to other errors. If I got it right that error is caused by a timeout from the nvidia driver waiting for the GPU.
https://forum.level1techs.com/t/is-my-graphics-card-dead-or-am-i-missing-something/161787/5 I also found this and the pattern looks awfully close to the one I usually had (at least on errors during runtime). Found that by looking into the "Graphics Exceptions", like that one at "[ 9.934829]".
I feel like using a live USB doesn't really help much since those freezes are very random and there is quite some time in between some of them. Furthermore I used the same hardware setup with preeetty much the same software on arch before and the same error occurred as well. Although testing an installation without any nvidia drivers could be interesting as well. It wouldn't really solve the problem though because I kinda want to use them (initially I wanted to buy an AMD card anyway, but I didn't find a good one for a decent price). The issue could also be caused by some other components not playing nice with the nvidia card but I don't know how likely that actually is.
My only concerns were that I pup on to little thermal paste. I'm not good at estimating sizes and distances and wasn't sure if I got it as stated in the manual. I'll probably put that at about the end of the list of things I want to check.