Same here. I see several have this issue, but have not seen a solution. I submitted feedback on the issue and will update if I get an answer.

I  could not get Synapse 3 to switch profiles either (Windows 11, never tried  on 10)

I uninstalled it and downloaded the Chroma Beta App. In that app is a link to download Synapse Beta. I could not find the link for that on the website that guides you to Synapse 3 instead. 

So I used Chroma Beta to download Synapse beta and then it wouldn’t even change colors through either app. So I uninstalled Chroma Beta, leaving Synapse beta installed. It works perfectly this way. I only have 1 device (Tartarus V2) so I don’t know anything about anything other than getting it to switch profiles and working as I intended.