Where do you see gradual decline? There are more macOS games than ever.
This is very much true — but this is not any different from how things were a year ago or say, five years ago. Mac gaming was always a small niche and only 10-20% games on Steam have a macOS version. This didn't change in the last decade or so, although the number of high-quality games have been steadily increasing.
This is absolutely true, there are more computer games available on the Mac than in its history. I think a lot of folks here are either too young or weren't Mac users during the "bad old days". I didn't switch from Windows to Mac until late 2005, but I had always been curious about the platform. During the worst of times, the Mac had market share of between 1% to 2%. I don't mean the gaming market, but the entire PC market. There were only a handful of ports from PC, they took up to three years to be released after the PC version, and would cost the original retail price, whereas the PC version could be had for a fraction. (For instance, as a PC user, I remember being astonished that it took two and a half years for the original Baldur's Gate to be released on the Mac, at full retail price.)
Today, with multi-platform engines such as Unity, we often get a simultaneous releases on PC, Mac and Linux. Even high-budget games that get a Mac version take significantly less time and tend to have the same pricing as the current Windows version.
As much grousing there is about Mac gaming right now, compared to the past, Mac users have far more choices than they once had. It's not even close.