Maybe more relevant to private data, the builtin wiki makes a good personal knowledge database.
The next version of fossil will have a forum (seen already at https://fossil-scm.org/forum/forum ). With the time sorting for threads, that might be good for temporal data that you wouldn't want to put in a wiki.
For my purposes, I don't see any advantage of Perkeep over Fossil. I know when I use Fossil that I can trust my system and that I will always have control of my data, and that reduces my stress levels. I have enough things to worry about without worrying about my data disappearing.
I don't use the feature very often, but Fossil supports unversioned files, which allows me to delete a 500 MB file from the repo if I no longer need it.