@mubh
To add the default tree, you can run
# 66-tree -ncE default
# 66-env -t boot boot@system
# 66-enable -t boot -F boot@system
Then populate the default tree. You need at least these services:
acpid dhcpcd dbus logind syslog-ng
plus your network manager, if any, and any other services you are using. You can add just those listed services using the command:
# 66-enable -t default acpid dhcpcd dbus logind syslog-ng
# 66-all -t default up
If you need to add pipewired to the default tree, the commands are:
# 66-enable -t default pipewired
# 66-start -t default pipewired
Update: Information on how to create "boot" and "default" trees from scratch is added to the wiki entry on suite66 (TL;DR section at the top).