Just wanted to confirm that on Debian Trixie, with the Flatpak version of OBS, Decklink cards (at the least the Decklink 4K Extreme 12G) will work, as long as you have given OBS all the device access permissions, thus negating the sandbox, but this shouldn't be much of a surprise with regard to Flatpaks generally.
Go to the Blackmagic Decklink webpage here:
https://www.blackmagicdesign.com/support/family/capture-and-playback
Then download the most recent Desktop Video Manual from the middle column under Latest Support Notes.
The Linux section is deceptively brief, with the bulk of the instructions being found in the ReadMe located in the Desktop Video tar.gz (located in the left column under Latest Downloads as the same page you download the Manual). Make sure you click the Linux icon for this one, and then note you DO NOT need to fill out the form, the bottom left contains "
Download Only" in a sickly, emaciated font, as not to draw your attention.
Get through the various levels of containers until you find the ReadMe file. It is structured oddly skipping back and forth between Debian and RPM based (Fedora) instructions with some sparse, less than helpful instructions(?) for the, "Other" distros randomly througout. I found it helpful to delete all of the instructions not pertinent to my use case (Debian) so that I would have one continuous document that wasn't jumping from distro to distro the entire way down. Read the Known Issues at the very bottom of the document firts. You may be disqualified out of the gate and be wasting your time in even making the attempt (see CET/IBT). The FAQ towards the end is basically the check to ensure you built and installed everything properly, not an actual FAQ, so don't let the naming fool you, you need to do the confirmations provided in that not-a-FAQ section. Follow the instructions and requirements to the letter throuoghout or it will not work. Secure Boot and the MOK security kabuki threatre are NOT optional. You too must embrace the saftey and piece of mind they will bring you. Be thankful. All is well.
Absolutely no plugins are needed from any random githubs or other outside code. I can only speak to the Debian side of things.
Enjoy your recording and or streaming and interesting new boot up scrolls.