I just updated an app that removes a feature which I relied on.
Now I want to bring back that former version, but I don’t have a Mac or iTunes available to do that.
So how is it possible to install an older version of an app using only an iPhone and/or iPad?
Unfortunately, no.
If you had previously been using something like iMazing, then it might have had a cached version of the previous version that you could reinstall, but barring something like that, there’s no way to roll back an iOS app update.
Works with versions in TestFlight as far as I know. If the developer is using it and has any beta builds at all.