android customization/theming apps?

cross-posted from: https://lemdro.id/post/44216782

i really like to customize and theme android, but it feels like basically all of the big boy apps are closed source and probably track the living shit out of you

any apps that are FOSS and doesn't steal my data?

NOTE: im not paying for anything, i know that disqualifies alot of apps but i just want something free