Update: it seems like it was indeed an issue with corruption due to the gallery. While browsing through builds in the gallery, my PS5 suddenly showed a bright green screen, then shut off. When I turned it back on, it went through a storage repair process. When I started the game, my save files were thankfully unaffected.
This is the third time this has happened to me. The first time was on my old PS4 and now it’s happened twice on PS5. Each time my save files were unaffected, but the first two times wiped my library clean on the gallery. This time, my library is still intact, so I hope it doesn’t happen again soon… I think at least one of the previous times was related to the flickering issue in Evergreen Harbor, but that hasn’t affected me for awhile now (maybe it affected the lots that I downloaded though).