Counterpoint: you'll stop enjoying a new hobby, like learning to play the guitar, when you decide to get serious about it.
In my experience this is more related to treating the hobby like a chore or job instead of doing it for the fun of it, even though you're bad at it.
I think the relationship is kinda the other way around - you'll feel like your hobby is "serious" when you stop having fun with it.
This hasnt my been my experience. I continue to love basketball despite being bad at it for years regardless of how much "serious" training I do.
Been writing code for 25 years, 15 professional. Still enjoy it just as much.
If it turns into treating it as a “should” then my experience is yes, definitely, that’s a death knell for basically anything. Without the “should” it continues to be fun. The trick is threading that needle.