In that other thread I detailed a while back my investigation to try and make gpg2 work inside a snap.
TL;DR: I didn’t succeed, I identified a number of changes/additions that would be needed in the gpg-keys interface, and I also identified incompatibilities between the versions of gpg in xenial and bionic that would require additional logic for the snap to talk to gpg-agent on the host.
At the time I was testing with a core16-based snap, built on xenial. It would be worth revisiting the problem now that the libreoffice snap is based on core18 and built on bionic.