I think most "I want to make an engine so I can make games faster" people are cursed to make engines forever, this is rare.
Anyone that wants to build an engine (or a CMS, or whatever) with the goal of making a game should try making one or more games with one or more existing engines first, if only to get a better idea of features and shortcomings. And if they really want to make games, or just the engine.
* Be resources efficient (memory and cpu usage)
* Has primary 3D support
* stable
* Supports old devices (ideally embedded systems too)
* And of course be FOSS
I'm focusing on mobile, as you know mobile devices are very sensible to heating so the 1st option is a must, Godot isn't resource efficient, it heats very easily when I play one of the sample games. Regarding the second option, whilst Godot still supports gles2(which is the most widely supported api yet across old devices) it's further being pushed as second-citizent over Vulkan and looking through github no other engine checks my boxes...
If someone could direct me to an engine that checks all the boxes above I would happily try it out.
Solution: make a new engine
Result: I want an engine that does x, y and z but none of the 5 can do that
but hey, your engine doesn't need to be a competeing "standard" if you do want to make a new engine.
the main up/downside is that it's a C# engine. So it won't necessarily be as hyper-optimal as c++ without some discipline on what parts of the language you use (hint: avoid LINQ at all costs in the hot loop, and look at the newer ways in C# on how to utilize unmanaged collections).