jrnl is a CLI tool worth mentioning when it comes to journaling, but does not cover your listed needs.

What free software alternatives are there?

Disable YouTube app from opening URLs. Use Firefox + uBlock Origin instead. No ads.

https://github.com/Fr4gorSoftware/SecScanQR

SecScanQR can not scan from an image.

Many phones specifically blow fuses in the device to make sure that attempts to downgrade will fail for security reasons.

I think you are mixing e-fuses (Samsung) and tamper-evident storage (Pixel). First one is used to lock Knox after rooting, second one to prevent downgrades.

Can you elaborate what the risk is?