From most preferred… CrDroid, EvolutionX, LineageOS, Bliss ROM.

I have had several Redmi phones. Yes, the current unlock process is a convoluted - You need a Xiaomi account. Then you need to toggle “unlock” in Developer settings. Then go to fastboot. Then while connected to your PC, you need the Xiaomi Unlock app to unlock the phone which you need to wait 2 weeks to happen. After 2 weeks, you go back to fastboot and the Xiaomi app, click Unlock and it is done.

(phew!)

It is tedious but not horrible. Once this is done, your bootloader is unlocked. You can then install your own custom recovery, custom rom, etc.

Redmi phones that have Qualcomm processors. Check out XDA forum for which models are supported.

There is no custom rom for this and there won’t be. It uses a MediaTek SOC. The bootloaders cannot be unlocked.

You can use bitwarden for passwords.

Sync what you can based on your threat model.

I backup what I can into a folder and then sync that to my backup drive. There are no way to backup app preferences without root.

Install Hypatia on fdroid and do a scan of your phone.

Check out Simplewall. Simple enough and not complicated.

https://simplewall.en.lo4d.com/windows

Many of them are on Telegram. Try looking for the groups by device name.