2018 Mac mini cannot display 5K on ViewSonic VP2788-5K monitor

Apple's specifications say that Mac supports "One display with 5120-by-2880 resolution at 60Hz" at the expense of cutting the total number of monitors that you can have from three, to two.

I couldn't find an entry on the ViewSonic site for that monitor, but the B&H Photo Video – ViewSonic VP2788-5K Overview page indicates that it is a Thunderbolt 4 monitor that supports 5120x2880 resolution at 75 Hz. I would expect your Mac to limit the refresh rate to 60 Hz.

As for the processor in your 2018 Mac mini, MacTracker indicates that it is an ntel® Core™ i7-8700B Processor. That processor has three integrated GPU outputs. ViewSonic is correct that no single one of the integrated GPU outputs supports 5120x2880 resolution. The way Apple got around this with their own 27" 5K Studio Display (the first one, from a few years back) was to send two video streams over a single Thunderbolt 3 connection. Each of the streams carried enough information to refresh half of the display. This is why connecting a 5K display cuts the total number of displays that you can have from three to two – the 5K display "consumes" two display generators.

If ViewSonic's monitor does not support this mode of operation, one possibility might be to try to run it in picture-by-picture mode, with two connections to your Mac mini (e.g., USB-C to DisplayPort and HDMI to HDMI), each for one half of the picture. You would then use extended desktop mode on the Mac mini to logically "glue" what the Ma mini saw as two independent screens back together.

In addition to Servant of Cats reply, most vendors ship inferior rated TB/USB-C cables with their displays.

It's not cheap, but I would be inclined to test a real Apple Thunderbolt 4 or 5 cable with that setup to see if it will produce 5120 x 2880 at 60Hz.

Thanks for both your replies gents, very informative.

I see B&H is a US retailer. It's on ViewSonic's UK website and I bought it from a UK retailer. Under Specifications on that web page, it gives the refresh rate as 60Hz but that's entirely adequate for my needs, as is having a single monitor.

I don't have a USB-C to DisplayPort lead, nor a better Thunderbolt lead than ViewSonic's, but I can certainly get one or both and experiment. I think, though, that initially I'll ask ViewSonic whether they support two streams over a single Thunderbolt. I suspect they don't, and that's probably where the problem lies.

It might take a while to get 5K to work but I think I'm now heading in the right direction: forever the optimist! Thanks again, guys. I could of course buy an up-to-date Mac mini but the M6 is eye-wateringly expensive.

I’ve been experimenting with picture-by-picture, using ViewSonic’s Thunderbolt lead and an HDMI cable. It almost gives me what I want but not quite. It gives me two screens on the monitor, each 2560 x 2880. Settings, Displays allows me to define one of the screens as Extended but, whichever I choose, the other automatically becomes Main; I assume that’s normal behaviour. I also found a recommendation to turn off the option in Settings, Desktop & Dock, Mission Control, of ‘Displays Have Separate Spaces’; apparently it makes the extended workspace more unified.

Having done all that, I can drag a window anywhere I want across the whole monitor. That’s the good news. The bad news is that if I click on the green Maximise button of any window, it only fills half the screen, not the whole screen. Similarly I can only expand a window as far as the edge of its half of the screen. Am I missing a trick with picture-by-picture settings?

I’ll ask ViewSonic if the monitor supports two streams over just Thunderbolt but I’m pretty sure what their answer will be.