Did the upgrade plan include an option for monitors along with the desktops? Given the form factor, a PC+Monitor+Mount option would have been a good choice, or an All-in-One with comparable specs. If the systems you were upgrading couldn't support 10 well enough to be usable they had to be in the 7+ year range of age, or really terrible even new.

I'm looking at the HP website, and the only mini I see with UHD610 is the pentium or celeron buildout, did your client really go with that? Pentium CPU's instead of Core series? Seems kind of terrible, especially when you've got this available: https://store.hp.com/us/en/pdp/hp-all-in-one-22-c1035z

Faster CPU, more ram, integrated display, and cheaper.

But anyways, yeah, I don't see a good way to deal with this since you're doing a digital-to-analog conversion from an underpowered budget cpu to an Ancient-AF monitor. If any of the monitors in question have a DVI plug you'll get better results, I don't know that I've seen an LCD monitor made in the last decade that didn't also support either DVI or HDMI.