@galgalesh - the personal-files interface is typically used to provide read-only access to top-level hidden data directories within a user’s real home directory in order to support importing data from existing applications where the snap is the clear owner of the target directory. Krita is the clear owner of ~/.local/share/krita/, so read access would easily be granted.
For write access, is krita’s resource manager forwards and backwards compatible such that on a system with krita from traditional packaging and krita as a snap are both installed, but with different versions, can the snap break the system’s krita or vice versa?