I ran into the same issue on Ubuntu, and the solution in this thread worked perfectly for me. For anyone else encountering this after an update:
Each new Itch version creates a new folder in ~/.itch (e.g., app-26.2.0).
The chrome-sandbox binary in the new folder will be owned by your user by default, so Linux ignores the setuid bit.
To fix it, run:
sudo chown root:root ~/.itch/app-*/chrome-sandbox
sudo chmod 4755 ~/.itch/app-*/chrome-sandbox
Using the * wildcard ensures it works even with the newest version folder.
After this, Itch runs without --no-sandbox.
It would be great if future updates automatically set the sandbox permissions, or if the installer handled this more transparently , especially since new versions break the sandbox by default.