> Office-jet (as most inkjets) don't understand
> postscript - you have to go over Turboprint.

Not necessarily:

"Drivers are represented using PPD (PostScript Printer Description) files, which support both Postscript and non-Postscript printers. [...] PPD files for Postscript printers will be added and they are ready to work. PPD files for other printers (PCL/SPL/ESCPR) contain reference to filter file (actual driver which translates data to printer binary format)." (emphasis mine)
https://library.morph.zone/Print_System

"Added driver for HP PCL5 printer"
https://www.morphos-team.net/releasenotes/3.12

So if his OfficeJet printer speaks PCL5, he should be able to cope without TurboPrint and use the new (since MorphOS 3.10) printing system instead.

> install Ghostscript

https://morph.zone/modules/newbb_plus/viewtopic.php?forum=11&topic_id=12813&start=7

> it makes much more sense, to user printers, which understand PCL [...]

There's a chance his OfficeJet printer does exactly that, I think.