HP has not provided driver support for the 6MP since Mac Classic OS 9, so over 20 years ago. There is no driver solution for macOS Monterey. HP has no driver solution for the LaserJet 6mp on its latest release of the HP Linux Imaging and Printing driver. The last Windows driver was for 64-bit Vista. And finally, the GutenPrint 5.3.3 release for macOS does support the LaserJet 6mp — however, that software has not been updated since Fall 2019 and was intended for macOS Catalina, not Monterey.
You would be better served, without headache, if you just acquired a new wired/wireless print that is supported in Apple's built-in AirPrint, or that states this on its box or advertising. Or, is currently supported by its vendor for Monterey. Neither the past nor HP cares about your ancient printer's compatibility with modern operating systems.
I took a workhorse 20-year-old LaserJet 4MP (Mac model) to the dump because drivers were getting scarce, and I had to guess whether a $90 toner cartridge or replacement platen (if I could find one) would cure the printing issues. I moved on…