I'm a happy user of open-tv who wanted the ability to create custom named playlists independent of provider categories in addition to 'favorites'. I developed this with AI assistance (Claude/Anthropic MCP). The architecture uses a source-agnostic join table so it works across M3U, Xtream, and custom sources without touching existing functionality. It creates an additional button in the GUI front with a drop down list for create new list and shows any created lists. I have that working in linux Mint 22.3 and 21.3 as an appimage and an installable .deb file for my own use. I have it in my git as a features fork. If interested, I am happy to adjust anything to fit your coding standards. Cheers and many thanks for your efforts!
[EDIT]. I made a new repo https://github.com/oldgranola/Fred-tv-plus which contains my additions for custom lists. There is also a new flatpak version there. In making that, I am not intending to step on toes or take over, just needed a rename there to keep things straight for myself. The flatpak worked for me in Linux Mint 22.3 and 21.3. The latter needed installation of org.gnome.Platform/x86_64/48 which I did via flatpak. Need testing in updated Ubuntu. Note: I do NOT plan to publish on flathub or AUR.