Not really a solution to what you need, but you should consider distros other than manjaro, it does some shady stuff, has ddos’ed the AUR multiple times (even though the AUR is “unsupported”) and let the security certificates for their site expire (their solution: to turn back your clock to update the system). You should try endeavour instead.

1. Not outdated

2. That’s the standard method

3. What features?

4. AFAIK it dods

5. Just don’t install the old apps then.

6. That’s literally why it was made. To distribute FOSS apps.

With tbis update system, I don’t understand why you can’t use your phone while doing it.