Having owned a 19 and a 21 Newmar with basically no issues. I do not believe there is a difference in quality between a 2015 newmar and a 2020 and up.
Having owned eight rvs I rarely had too serious an issue myself. That could be because I try to fix or do preventative maintenance and I accept that they are rolling earthquakes and stuff will happen.
If you truly read most of the issues the last few years, most can be attributed to operator error. I see complaints about the simplest things. Literally one person complained because they had no idea how to tighten a tp holder, a residential one, and four responders said, Newmar quality has gone down, really! I think the majority of buyers years ago were more of a hands on type. Also, remember today we have a multitude of forums, facebook and other groups. Back then we did not. Nowadays I notice people cross post the same question on a few forums and a few fb pages. Those actions seem to falsely multiply the idea of numerous problems.
Then when they post, they get a large number of answers that are blatantly wrong. Which adds to the mystique that there are a major number of issues. And the fact that many owners a not handy.
How many times have you had an issue only to find out you were not operating it correctly? It happens, we are all guilty of this to some degree.
Are there issues, yes but I do not believe there are any more then ten years ago, its just now that there are more places to post, hence more places to see the same complaint with different poster names.