We had a similar situation with a Grand Design transcend we bought new in 2020. One problem after another. We were permanently set up in a park and couldn't take it in for service. GD wouldn't pay for mobile service calls so I ended up making most repairs myself. Seems like I spent all my time at the camper doing repairs, no time to enjoy camping. I wrote a 5 page letter to the President of GD stating that we got a lemon and asked for a refund or replacement. They would do nothing. I ended up repairing all known problems and sold the unit. I would never buy a new unit again. We now have a used 2019 unit and I fixed a few minor problems when we first got it, but for the most part we haven't had any problems on our our trips since then. Enjoying camping again!
I understand your frustration, but buying used isn't always the answer either. I moderate on a major RV forum, and monitor several others. Sometimes the "gently used" unit that you buy is just another "problem child" that someone else had dumped (like yours).
Either way, I'm glad that it's working out for you.