Glad you got it fixed.

It appears to me as there are several problems that are not at all obvious.

The Mint version you are using was messed up, why else would you need to remove and re-install so much of the system. The term "plugin" to me is misleading. Software for scanners are called "backends" by the rest of the linux world. That caused me to ignore that term. ( BTW I don't run Mint ) so its easy to get misled.

HP could do a better job at showing support for their multi-function devices. The printer was working, not the scanner. In the end, HP's HPLIP does in fact support both devices. That is not at all clear on the page showing the software support for linux.

This has been a learning experience for all involved. Thank-you for posting a clear fix.

Yes, that does seem to be the case. I've noticed a few Mint threads where a similar rip out and replace was undertaken to get a working HP printer/scanner.

The plugin and scanner backend are two different things. HPLIP provides the 'hpaio' scanner backend, but it does rely on having a correctly configured 'hp' printer URI for communication. The proprietary plugins are used for some HP models, and required for printing and/or scanning support. From the page reference below, I see the HP Color LaserJet MFP m277dw requires it for scanning...

https://developers.hp.com/hp-linux-i...ry_plugin.html

For future reference: I got the HP Color LaserJet MFP M377dw to work on Manjaro by installing sane, xsane and simplescan.