Have you tried altering the limits through the Support Settings? If not you can go to
Settings → Support, and then in the Support Key field write limits.single_field_size_bytes:. This will give you a new field where you can enter your 65000 value and save it. I had to do something similar for my case and it worked. Hope it helps!
With Dremio-Cloud, I don’t have access to the “support” page where I would be able to enter configurables like this one. As I understand it, someone at Dremio has to do it since they need to maintain pretty tight control over these kinds of things.