Traceback (most recent call last):
File "/usr/bin/mypaint", line 309, in <module>
main.main(
~~~~~~~~~^
datapath,
^^^^^^^^^
...<4 lines>...
debug=debug,
^^^^^^^^^^^^
)
^
File "/usr/lib/mypaint/gui/main.py", line 133, in main
lib.glib.init_user_dir_caches()
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^
File "/usr/lib/mypaint/lib/glib.py", line 193, in init_user_dir_caches
k.value_name,
^^^^^^^^^^^^
AttributeError: 'UserDirectory' object has no attribute 'value_name'
Since it is in the official repo - packaged by Arch Linux - I suggest you update your system and use the repo version of mypaint.
$ pamac info mypaint | grep -e Version -e Packager -e URL
Version : 2.0.1-6
URL : http://mypaint.org/
Packager : Jelle van der Waa <jelle@archlinux.org>
If that does not help - you will need to go upstream to the developer(s) as specified in the URL.
MyPaint developers promote the use of their flatpak - try that method instead - you will likely solve your issue that way.
Remove the repo version
sudo pacman -Rns mypaint
Install the flatpak version (you may need to install flatpak too) - if you are using plasma - you may want flatpak-kcm as well