We've been suffering this problem for years. We've mostly got around the problem by asking the users to set the keyboard mode to Unicode, which allows enough of the UK Mac keyboard to be mapped as the average user needs, including the '@' sign and speech marks.
However, as developers we use Scancode, which allows us to do things in calculations that Unicode doesn't. We've uploaded a custom UK keyboard to each RemoteApp server, which again does an OK, but not perfect job.
Now we have a problem for users authenticating by OAUTH 2 for Microsoft 365 within our apps. Typing into a web browser within FileMaker using Unicode results in a 'Before typing, press Tab or click in a field' message, which is a standard FileMaker error when trying to enter data without having the cursor in a field. However, there are no fields in this case, just the native Microsoft Edge engine based web viewer.
Swap the setting to Scancode and all works fine, except the keyboard mappings then rely on the custom keyboard, which has to be selected within a floating language bar and set for each session (if it opens at all, or with the text displaying to change it, which is the most common annoyance).
We're now playing with modal window settings to see if we can get around this (once again).
For years Jump Desktop from PhaseFive Systems has allowed a 'Match Mac Keyboard', or an extensive list of international keyboards, to select from for each connection. It is very obvious that this is not a priority for Microsoft, despite the awful user experience outside of the US.