This may seem kind of weird but simple and obvious to some.
As most of us know Borderlands 3 is having some issues post-launch with performance and other bugs. I downloaded the game on a Seagate external hard drive. While playing the game I was experiencing so much lag that made the game unplayable even on an xbox one x. When entering new areas and encountering a group of enemies I couldn’t move, zoom in or switch weapons without a 2-3 second delay. Even while playing in someone else’s game it was pretty bad until I just wanted to try something…
I moved all of the borderlands 3 files to the internal hard drive and to my surprise no more lag. After that I’ve had no issues at all. I don’t know if moving it to the internal hard drive has anything to do with it (compared to an external that runs at 5400rpm I doubt it) or just simply re-installing the game helps.
I hope this post helps and I wanted to keep the backstory short so readers could get to my solution quicker. Have fun and go get that loot!