Bazsl, you're right. The advice you got works in Mac but not Windows. Also having wasted time on this, I feel your pain. If you want to try one more time, it will only take a few minutes, and the following will either work or not for you. You'll have to go back to the Creative Cloud app and install beta Photoshop again.
Here's the deal: in MacOS, you can easily choose which installed version of Photoshop (PS), whether regular, beta, or an older version of PS you want to use from Edit In in Lightroom Classic (LrC)... at least after changing the External Editor Settings. This is what you see demonstrated in some YouTube videos and help advice online. They're using MacOS.
But after you download and install the beta version of PS in Windows, at least as of April 2024, if you use the Edit In command in LrC, you get no choice of PS version, you can't change it in LrC's External Editor Preferences, and the file opens in regular, not beta, PS. So how do you use beta PS from LrC in Windows??
You have to do a workaround one time only. In Windows open the Adobe Creative Cloud app. Go back to the Beta tab where you installed the beta version of PS. Once Beta PS is installed, the "Install" button says "Open" instead. Click "Open" for Beta PS in the Adobe Creative Cloud app. Beta PS opens. Leave beta PS open. Also open LrC for Windows, choose a file, right-click and choose Edit In > Adobe Photoshop. The image will open in beta PS. It may just say "Adobe Photoshop" with no mention of "(Beta)" from the Edit In choices or in External Editor Preferences, but it should open in beta PS. You can verify that it did by clicking in PS: Help > About Photoshop and check out the version displayed there.
In future edits, after one success as above, you should not need to use the Adobe Creative Cloud app to open PS first. Just use Edit In from LrC for Windows as you did before, and it should open automatically in beta PS. If you want to go back to regular PS, as you may want to do once regular PS includes the beta features you want, just uninstall the beta version of PS from Windows, and only if needed because using it is not an option in LrC, open regular PS first in Adobe Creative Cloud, or if needed reinstall regular PS in Windows from the Adobe Creative Cloud app.
LrC in MacOS handles this much better than LrC in Windows. Who knows why?? Not me.