Either way, this is putting me in a serious dilemma. I have software that is no longer compatible with 10.13 that I use for work. I can't update OSX because I have an Nvidia 1080ti. I am hesitant to spend a large amount of money on an older generation AMD card without knowing what is happening with this series.
Same boat as you. I am a pure Mac user so no need for Windows. I built a hack in 2018, the first one and probably only one. Reason, for around £3k I could risk building a setup that would outperform what Apple could sell me at that time.
Previously I'd buy a new iMac every 3 years. But my work got more demanding regarding graphics power. The HS 1080 build I use is rock solid but during the last few months all my software updates are becoming incompatible, Davinci, Blender, most Adobe apps. I pay for Adobe's CC, which is annoying but at the end of the day it was my choice to risk building a hack for work purposes. It's feels a little dirty, but the horsepower and hardware options are great.
Given the current incompatibility of these new AMD cards (my hunch is they *may* be supported much further down the line, more on that below) and the fact graphics cards are so ludicrously expensive + hard to come by and probably will be for the rest of the year if not beyond, my options are to wait for a suitable M* iMac that will have enough graphics grunt for my needs. Or hold out for a M* MacPro. Considering the work I do, switching to Windows would be the best thing to do, but f that.
A few months ago I was certain these cards would gain driver support pretty quickly. I've now changed my views, not least for the obvious reason that we still don't see support. If you consider the top whack x4 GPU graphics config for the Intel MacPro it's extremely powerful, albeit stupidly expensive. How many higher-end MacPro customers are desperate to upgrade beyond the current upgrade options or indeed if they already have the top spec? Likely most of these customers are perfectly content for now. It still leaves a hole in the market, for pro creatives like myself. I think this will be addressed when Apple unleash more powerful graphics systems. I strongly feel they are working on something that will be sufficient, but realistically this will be a 2022 thing. Happy to be wrong.
I impulse bought a 6900XT in Jan but sent it back within 10 days as I don't use Windows and reconsidered the insanity a £1200 paperweight. Supply seems to have got worst since, no doubt the recent crypto boom is partly to blame.
All said, agree with some others comments on here to just be hyper aware if you're considering buying a new AMD card specifically for MacOS you're probably in for a long wait.