Iirc there are some that are literal direct ripoffs (exact same sets with a ELGO or some obvious ripoff brand) that appeared at a time, and were pretty obviously run off of a Chinese Lego line (I believe Lego got them shut down by winning a copyright case in China).

The quality of off-brand is way up in the last 20 years but it’s still not the same; they run the molds way too long.

Just to add my own two cents: Cobi produces exclusively in the EU and with superior quality than Lego, albeit focused mostly on adult market with military stuff.

There is Mould King, Cada, Bluebrixx which also have more decent sets but you need to do your own research and specific sets. Newer sets are generally higher quality than older ones as Lego competition as drastically improved in recent years.