There's also a difference between rolling your own in-house engine like Frostbite or REDengine, and making a game on your own with no general-purpose engine using something like SDL. There's little point in doing the former nowadays, but there's plenty of titles that still successfully take the latter approach. General-purpose engines make this whole field obviously more approachable and for some kinds of projects are the only viable option, so the percentage share of no-engine games will likely continue going down, but I don't expect absolute numbers to drop significantly.
On Steam, it seems to be about 20% - pretty much the same share as Unreal's: https://www.gamedeveloper.com/business/game-engines-on-steam...
There's also a difference between rolling your own in-house engine like Frostbite or REDengine, and making a game on your own with no general-purpose engine using something like SDL. There's little point in doing the former nowadays, but there's plenty of titles that still successfully take the latter approach. General-purpose engines make this whole field obviously more approachable and for some kinds of projects are the only viable option, so the percentage share of no-engine games will likely continue going down, but I don't expect absolute numbers to drop significantly.