Kestrel is about 28mb max by default, but when I change Kestrel to accept up to 6gb, then my next problem is I cannot seem to upload any files larger than 2gb

I guess there are more limits in the chain between the user and the server. Maybe a browser limit? Provider limit? Is there a proxy between the user and the server?

hum, ye there must be. I didn't consider browser limits. Its an Ubuntu VPS from IONOS and nginx, no proxies.

There may also be request timeout limits as well, if you are uploading a large file, the request may potentially break

Have you tried multipart uploads? Might be hitting HTTP Request size limit

Maybe some limit in the infrastructure, do you have any revers proxy ?