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Maybe it's because you have too many mods on your device but It's just my theory please don't take offense.

I suggest deleting all the attempted installations to begin with. If you haven't already, follow the Installation Guide for Android users, provided by Elena:
(If you're still having problems, let me know)

Install instructions

For Android users!

Go to Google Drive and tap on Gacha Neon.apk. The installation will start.

⚠ Attention

How to fix "app not installed" (Link)

Dellt dev, the author of Gacha Redux, told me how to solve the "can't install" bug. Thank you very much.

1. Go to your device settings and tap Apps & Notifications (or Apps in older versions of Android).
2. Tap the three dots in the upper-right corner.
3. Tap Special access.
4. Tap Install unknown apps.
5. Tap Chrome (or whichever web browser you use)
6. Move Allow from this source to the On position.