Godot.
Totally opensource, totally free, 2D and 3D, being actively further developed and refined all the time.
I can develop on Godot on a Steam Deck... theoretically, you should be able to run Godot on another ... non standard pc hardware configuration? Both a Deck and a Snapdragon laptop use shared LPDDR5 RAM, as ... well Valve calls it an APU, Snapdragon calls it an NPU, basically, the CPU and GPU just literally are the same physical chip.
Only downside I can think of is that Godot might not be 'the simplest of simple'.
If you want... even more simple...
... maybe consider LÖVE / LÖVR.
Balatro was made in the 2D only LÖVE, and LÖVR is basically the 3D version of it.
Its all buuilt off of LuaJIT, which means its basically all coded in Lua, a bit simpler and easier to understand than the python-like GDScript of Godot, and that Lua basically just gets automagically converted into C(++?), via the built in LuaJIT compiler.
Uh, tl:dr; LÖVE / LÖVR are probably? the simplest and easiest way to do 2D and 3D as a beginner, Godot is a bit more fleshed out, but also more complicated, both are totally open source and free to use.