On my freshly installed ubuntu 20.04.4, I also installed the LO suite as snap ~1 month ago. Everything worked fine.
Today after installing the recommended latest updates and patches to Ubuntu I suddenly could not open any documents in LO writer or create new. Calc and Impress seemed to work fine.
I solved the issue by fetching and installing the deb package with LO v 7.2.6.2 in which the LO writer works, but wold be nice if the bug could be found&fixed so I wouldn’t need to parallel versions of LO 