There is no snap in pop os unless you installed... Firefox and libreoffice are debs. The problem may be that the pop-desktop package is depends on too many packages, but not snap
I experienced the same thing (had previously uninstalled libreoffice, but it came back after the update). I didn't get snapd back fortunately (though I do use Firefox packaged by Pop).
Part of the change is that Pop!_OS is moving away from ubuntu-minimal and ubuntu-standard meta packages and towards their own metapackages as shown in this this recent commit.
After the update, I simply uninstalled libreoffice... hopefully it doesn't return in the next update :]