Like most such choices, it depends on how you intend to use it. I’m typing on a 1st gen iPad Pro 12.9 with 32GB of storage, and it hasn’t been a problem.
However, video files are big, and if you intend to edit video on an iPad, which can work really well, more storage might be helpful. But still, that depends on whether you have daily access to a laptop/desktop, or use cloud storage, because a single typical drone video project is likely under 5GB. If you want to keep a lot of video stored long-term on an iPad you could consider more than 64GB.
My son would always say “get all the storage you can”, he would want all his digital content always available wherever he is.
The cost premium to get up to 256GB seemed too steep for me. I just ordered a Mini 5 (currently discounted at Best Buy), and went with the 64GB version. Your mileage may vary! There are probably other reasons to choose 64 or 256, but that’s how it seemed to me in how I use a tablet.