Conversely, almost every android version I've downloaded runs fine.
First and foremost, what version of android are you on? What kind of phone do you have? The problem is that older android phones struggle with bigger Renpy games. My Note 10+ runs 95% percent of Renpy Android ports. Whereas my Note 5 won't even start or install a lot of them. An older phone may cause problems.
To your first point, Android isn't going to tell you that need to allow unknown sources if you've done it already. My phone asks that for each individual app that I sideload. So, it's certainly possible you did forget. If it's not asking you per app, I'd assume you're likely using an older/custom version of android? I'm basing that off of Samsung and their One UI, though. May be different for other brands.
Your second point, if I remember correctly, has nothing to do with creators/devs and everything to do with your phone. I believe that error comes from a lack of space. I could be wrong there, though. Even then, it's kind of a hassle to make Android ports for Renpy games, which is why you don't see a lot of official versions.\
As a last resort, you could always try
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.