FlexToTheos VS IGSideloadFix

As far as i know, you'll need to convert that FLEX patch into a regular jailbreak tweak (using something like https://github.com/ipadkid358/FlexToTheos. I'm not sure if there's a better alternative out, this is what I used in the past). Once that's done you'll use something like Azule (https://github.com/Al4ise/Azule) to inject that tweak into a decrypted ipa.

No, flex patches do not come in deb format. But you can convert them using tools like FlexToTheos and inject into the IPA. You can then send that tweaked IPA into any device and sideload it.

Flex3 can be found here: https://getdelta.co/, and FlexToTheos is available here: https://github.com/ipadkid358/FlexToTheos

https://github.com/ipadkid358/FlexToTheos - original flex to theos by iPad_kid

Not sure how easy it is but there’s FlexToTheos

Instagram requires Sign-In fix to create a sideload apk. You can find it here: https://github.com/opa334/IGSideloadFix

I don’t know how to patch Messenger. For Instagram Rocket, follow this: https://github.com/opa334/IGSideloadFix

for a better explanation, check out this git repo, it was the same situation for Rocket: https://github.com/opa334/IGSideloadFix

How to build Rocket for Instagram (credit: opa334)