I started building a game on a custom engine a few years ago and I used to think about selling it, but nowadays the market is so oversaturated I tend to think of it as nothing more than a coding exercise.
The market is oversaturated of mediocre games, but I struggle to find any notable titles in the past 5 years. 30 years I was pirating games I did not afford, in the past 15-20 years I bought all the games I played, but in the past few years I don't remember buying too many games because there was nothing interesting. The last games I bought were Cyberpunk 2077 (+ extension), an indie game (Forgotten City) and Stalker 2 (a disapointment).
If you build a really good game, there is a market for it. Otherwise it will be lost in an ocean of not-interesting titles.