Not very familiar with the topic, but that seems related to your issue. I suppose you didn't make a backup of
security_keys.txt
?
Restore that, or revert the read-only or simply delete the file.
You may/will get a new generated key, and get security warnings when trying to load a save. First you'll have to trust the save, then you'll get "do you trust the device the save was created on". When you say yes to that all your saves (that were signed with the same key) will be trusted so you won't be asked again.
Have a look at the top (best) comment of that thread. It points to an F95 post:
New Ren'Py Token Check (when creating a save) #20
Also (to whom it may concern):
Ain's punishment