If your main goal is to enjoy yourself, there are very few programming tasks as varied and fulfilling as writing your own game engine. Personally, I'm glad there are alternatives.
I heartily recommend PICO-8 for anybody trying to get into hobby/solo gamedev from the programming direction.
But seriously how do you fit a game into an 8-bit environment?
Don't be put off from writing your own engine, but it is quite a daunting task, expecially for 3D.
Besides rendering, these off the shelf engines provide tooling that make game development easier on you. Map editing, animation editing, sound editing etc all built in.
I am not sure if I made the right choice or not but the engine I’m working on is indeed very satisfying to build though I am aware I could have had a playable game by now instead of still be implementing hand cranked shader animations and trying to architect a custom rendering stack… but I figure if it’s not one thing it’s another!
Plus if you do succeed don’t you end up owing Unity a bunch of money?
Unless the licensing scheme changed, you can see the graph of licensing costs for Unity on articles like this one: https://gsnook.wordpress.com/2019/01/19/for-indie-developers... (specifically: https://gsnook.files.wordpress.com/2019/01/enginecost.png?w=... )
I wish you all the best, and primarily to keep your passion.