I upgraded to Triliumnext. It uses the same database, but...
I had an 'up-to-date' Trilium installation *according to the entry on the Docker tab*, but when I tried the replacement Triliumnext, I hit a complete roadblock telling me Trilium hadn't been updated, so the database was out of date. Logs had "App db version is 228, while db version is 215. Migration needed." and "ERROR: migration failed, crashing hard." The latest Community Apps Trilium is version 0.54.3.
Solution was to update Trilium first - in UnRAID, that meant editing the docker entry to "Repository: zadam/trilium:0.63.7" (click to Advanced view to be able to edit this).
After that, it just worked