There are two places in the log which might be indicative, namely:
[2021-02-24T23:28:31+0700] [ALPM] running 'fontconfig.hook'...
[2021-02-24T23:28:31+0700] [ALPM-SCRIPTLET] Fontconfig error: Cannot load default config file: No such file: (null)
[2021-02-25T23:45:46+0700] [ALPM] installed lib32-fontconfig (2:2.13.91+48+gfcb0420-2)
[2021-02-25T23:45:46+0700] [ALPM-SCRIPTLET] Rebuilding 32-bit fontconfig cache...Fontconfig error: Cannot load default config file: No such file: (null)
This means the fontconfig installation hook is failing for some reason.
Also, not sure if related (probably not looking at the datetimes), but yay-git is a development version of yay, I would use yay instead:
[2021-03-17T15:14:10+0700] [PACMAN] Running 'pacman -R yay'
[2021-03-17T15:14:11+0700] [ALPM] transaction started
[2021-03-17T15:14:11+0700] [ALPM] removed yay (10.1.2-2)
[2021-03-17T15:14:11+0700] [ALPM] transaction completed
[...]
[2021-03-17T15:17:59+0700] [PACMAN] Running '/usr/bin/pacman -U /opt/yay-git/yay-git-10.1.2.r32.gece81fa-1-x86_64.pkg.tar.zst'
[2021-03-17T15:18:01+0700] [ALPM] transaction started
[2021-03-17T15:18:01+0700] [ALPM] installed yay-git (10.1.2.r32.gece81fa-1)
[2021-03-17T15:18:01+0700] [ALPM] transaction completed