Software version

There is one last thing you can try/attempt, if you need older versions of apps.

If you own another much newer iOS device that can run iOS/iPadOS 13 and later, you can install the most recent version app/s onto that more recent iOS device.

Then go back to your older iPad, open the iOS App Store, go to the Purchases section of the store app, search for the app/s you wish to try and download to that older iPad and see if an older version of the app is allowed to be downloaded/installed to that older iPad.

These newer iOS/iPadOS devices must use your same Apple ID user account and password.

What version of iPhone do you have? Sounds like you have an iPhone 6 or earlier. If that is the case, you cannot update the iOS on that device. If you need something newer than iOS 12.5.4, you will need to get a newer phone.