There’s already Flatpak, but it’s not on Flathub.
https://cdn.kde.org/flatpak/rsibreak-nightly/org.kde.rsibreak.flatpakref
https://github.com/KDE/rsibreak/blob/master/.flatpak-manifest.json
Project information: RSI Break helps prevent repetitive strain injuries by keeping track of usage patterns and periodically informing users to take breaks. During break periods, RSI Break can either show an unobtrusive message, lock the screen entirely, or present a slideshow.
Name: RSI Break
Homepage: https://apps.kde.org/rsibreak/
License: GPL-2.0+
Upstream has been contacted: https://floss.social/@nicofee/114465551488989987