RichardMH

This comes up from time to time .

can you post a screen shot of what you get?

There are a few youtube videos on this. Look for double exposure effect.

Windows or Mac?

If you have a supported camera (Sony, Fujifilm, Nikon), Capture One Express might be worth a look. Otherwise, NeoFinder.

I have a cheap monitor as a second screen and my Library, Assets and Macro windows live there. If I'm doing a lot of masking or selections, the Channels also go there. Gave up on waiting for macro hotkeys. Other advantage is if I'm going to post on the web I can see what most people will see (sort of, as my cheap monitor is also calibrated)

Do backups regularly with different names so you're not over writing a good one with a corrupt one (should it happen again).

AFAIK you need a calibrator or a light meter. Can use your camera or download a phone app but will need to do some conversions (and I'm not convinced the apps are reliable).

There's a bit of leeway. From a course I did there is a standard, ISO 3664:2009 Graphic technology and photography - viewing conditions (P2) recommends calibrating monitors to a white point of CIE D65 and luminance between 80cd/m2 and 160cd/m2 in a neutral ambient environment less than 32 lux. I think a lot of photo editors are between 100 and 120 cd/m2. But people viewing your images on the web will have random brightness. If you don't have a calibrator you can use your camera's light meter. First convert to EV here https://www.translatorscafe.com/unit-converter/en-US/luminance/6-1/ so 120cd/m2 is 10 EV. From the table on this one https://www.scantips.com/lights/evchart.html we then get 10EV is 1/60 at f/4 and ISO 100 (looking at white eg blank Word page)

As above, blend ranges lets you fine tune it.

Does the Shadows slider not work?

When I accidentally sent a ROMM RGB image to my local printer then e-mailed to say I'd made a mistake he said it was OK and he could print it. He has ink jet printers for art printing and wants RGB rather than CMYK. My home printer set up will print ProPhoto/ROMM RGB images.

As far as I know, ROMM RGB is the largest color space. I have that set in Color Preferences. For print I use Adobe RGB (1998) or ROMM RGB (a lot of printers can handle it) and for the web sRGB. I've been told to use the largest color space for editing then convert for whatever use, (and use soft proofing)

Might be gpu related. Somewhere there are posts on how to turn off hardware acceleration. But maybe update graphics drivers first.

I've been running on Windows 11 for quite some time with no problems. Sure its not your virus checker?