It depends on what platform. I usually check ratings of books on Goodreads and then NU when I used NU more. From a reader's point of view:
If its on Goodreads, 3.23-3.5 can be decent good novels. 3.5-3.8 are getting better. But 4.0+ novels are really good, usually see it never as high as 4.5 but example 4.03-4.23 kind.
If its on NU then its 4.1-4.2+ novels are decent. 4.2-4.3 starts to get be safe good. I do like more of 4.5-4.6 rated novels; those to me are a lot better and good. 4.0 novels is still an eh bit risky.
I kinda would base SH on NU. However, 3.5-3.8 novels on Goodreads is not that bad (honestly that seems good range if just starting out), and since this is site for anyone to start writing, perhaps 3.5-3.8 books are not too bad on here, but ofc, not as great as books with similar rating on Goodreads. I may not mind book on Goodreads that is mid 3 range like rated 3.5+ if I come across it by chance, but on NovelUpdates and probably SH, I like going for 4.3 or higher; although on both platforms, I generally go for 4.0+ rated books.
On NU/SH, 4.4-4.7 books are great. 4.2-4.3 books can still be a gem. Anything 3.9 below is not great, and 4.0 is risky.
On Goodreads, 3.5-3.8 books are not bad but can be decent good. Would skip 3.1 below if I do come across this. Not on Goodreads much.
Sometimes do I find novels that I feel should be rated higher, bc I liked the story. So it depends on how each feels about a novel. And it depends on the platform of ratings I'm reading on.
Now from a writer's point of view, I think scoring somewhere 3.5-3.8 is nice decent start, since barely just an amateur writer; even 3 is not too bad. But if it drops below 3.0, then I would go back and revisit to see why; anything 1-2.99 is low imo. But, goal of writing personally would be somewhere 4.1-4.3+ at least.