Agreed - if you are playing a file from the M.2, the data path is not the issue.
If playing from M.2, SD is a don't care.
H.264 reduces or eliminates the need for HW decoding.
Another don't care. RAM speeds are far above the video data rates.
This is probably the most likely.
Another ignorable concern.
You can try another test... record video on your drone, but set it to 1080p/60 rather than 4k. Then see how that plays on your system. If drone 1080p plays well, there's one more thing you can try.
Install Handbrake, and recode one of the failing 4k videos to 1080p (use the General/
Fast1080p30 preset). Then play the new 1080p version.
If all you ever want to do is play drone video on your PC, then just drop your captures to 1080p and enjoy. If you want to move up to 4k at some point, record 4k now and recode to 1080p for the interim - put the 4k files somewhere safe (external RAID1 NAS box - two drives, mirrored).
As a footnote, when I bought my EVGA 3080, I signed up at EVGA for their in-stock notification, and I was able to buy my card at MSRP at a time other sources like Amazon and BestBuy were selling the card for twice MSRP. The process worked well for me: sign up for the card you want, in a few weeks you'll get an email when the next shipment comes in - and you click a link in the email to buy the card. It ships the next day.
I got the EVGA 3080 FTW3 for the $870USD MSRP, when they were selling at Amazon for over $2500USD.
And you don't need a 30 series for HEVC or H.265 - a 10 series or 20 series will playback 4k video quite well.