Hi @rbgtoffolo,
The Flathub package is stuck at Processing 4.3, so it only seems to “fix” things because you’re installing an older version (pre 4.4) where the issue didn’t exist yet.
For a real fix, try Processing 4.4.6 or 4.4.7. They’re available as a Snap with classic confinement (which bypasses all usual snap restrictions) and should work correctly.
See Processing 4.4.4 on Ubuntu 22.04 can’t access tty ports - #8 by sableraph
PS: We are also working on adding an official flatpak build to future releases (see Revisiting the GitHub Actions Release system (.flatpak + .deb) by Stefterv · Pull Request #1204 · processing/processing4 · GitHub)
(Raphaël)