I found my root partition quickly (lets say daily, even hourly) full. took a look at the syslog and it was 18GB in size. took a look inside and it was full of two errors, one related to a specific Gnome extension (boom! disabled that, and wrote a comment on its github page) and the second:
Object St.DrawingArea (0x55f7cc178c40), has been already disposed — impossible to access it. This might be caused by the object having been destroyed from C code using something such as destroy(), dispose(), or remove() vfuncs.
of which I have no idea.
Ubuntu 21.10, Gnome 43, with the latest updates possible.