You might give Sideloadly and/or zsign a try.

Khodeus wrote: ↑Sat Apr 23, 2022 7:43 pm Yep, on jailbroken device there's no need to Altstore, unf my ios version does not allow JB :/

I don't know about AltStore but following the steps from the second post I managed to successfully install a working daily build with appinst/AppSync on a jailbroken iPad A10.

I think the OPs trouble is because a popular IPA signing app (AppSync Unified) is not working on iOS 14. It is possible however to just download the latest offical stable build as .deb-file, installing with dpkg and running uicache afterwards. Works fine for me on a jailbroken device.