I can send you the log of T970 twrp and I can make los recovery and pbrp for the tab s7, maybe that has an effect because there was an effect with pbrp on the tab s7+, the tab s7+ has a small glitching strip that appears sometimes but is barely noticable but in pbrp it appears wiith every interaction, I was able to lower it but I couldn't fix it. Sometimes other recoveries work better than twrp, for example the oneplus 8 lineage recovery works better than twrp. Somebody suggested me to build the kernel inline with twrp because samsung had issues in the past, I tried with all the firmware files for our device and it fixed the timezone bug but nothing else.At this point, I really want to think that the issue has something to do with how we're setting up/driving the display. I'm leaning away from it being an outright problem with the kernel (and definitely don't think it's the device tree), but I do wonder if the information in the kernel logs might help us find the problem.
In comparing logs from stock recovery (where video obviously works) with logs from TWRP, I can see some notably different values getting used for initial backlight/brightness settings, as well as some other differences related to the display.
Now, I don't know that the differences I've spotted actually matter, but the display in the T870 is obviously a different model than the larger one in the T976, where TWRP is functional, so it's certainly something to check at least. For now that's all I've really got, but I'll be digging into this more soon.