Hi, I'm Nico7550, I only know BigBox from name and I only register to add a comment.
After reading the first post, I understand the income problem and the technical problem.
But maybe the initial goal wasn't taken from the good side. Let me explain my point :
1.) Even if you have a frontend install on your everyday smartphone, the lack of real controller will force you to abandon playing after a while.
2.) Most of people change smartphone every 2 to 4 years, so if you take care of your goods, you have an old smartphone at least equal in power to a raspberry 4.
3.) Android is limiting according to first post
Why not change the pov. Made a frontend for abandon smartphone installing a linux on it to keep ride of the limitation ? After all the raspberry distribution are based on unix...
Have a nice day