I am seeing similar artifacts printing to an HP Color Laser Jet (CM 2320 nf MFP). The problem appears to be with the printer driver built-in PDF to PostScript converter in macOS as best as I can tell.
I tried:
1. printing from Affinity Designer (worst coloring, artifacts)
2. exporting PDF - for print and printing from Preview (improved - fewer artifacts and in different areas)
3. exporting PDF - for press and printing from Preview (same as for print but less noticeable)
4. exporting PDF - for press and printing from a Linux machine that doesn't use the driver (problem disappears!)
In all cases the files look perfect on screen. (My main computer is a Mac M1, running macOS Big Sur 11.5.2)
Update:
I have tested this work-around. Convert the PDF to PostScript and send the raw PostScript to the printer via Terminal using:
lpr -o raw < filename.ps
Unfortunately, you can't use the built-in converter in macOS file>print>save as PostScript (same artifacts). I got help with one on Linux but I'm sure there are others that will work on the Mac.
