The native client shuffles around the modifier keys on macOS in order to compensate for Alt behaving like AltGr on macOS. This has been around at least since bug 3599.
The same thing should be done in Web Access since Alt behaves the same there on macOS.
This got fixed for macOS when bug 6152 got resolved. However Web Access also works on iOS that also has the same need (at least when a physical keyboard is used).
Wrote release notes for this fix.
Updated documentation to describe Alt keys on macOS and iOS in Web Access.
Also fixed release notes to show that this behavior is new not only on iOS but on macOS as well.
Documentation and release notes look good.
Note that there are now some duplicate lines in the documentation for the native macOS client and for web access:
> The Alt key (also know as the Option key) behaves very differently on macOS
> and iOS compared to its behaviour on other platforms. It closely resembles
> the PC AltGr key, found on international keyboards. ThinLinc therefore
> treats these keys in a special manner on macOS and iOS in order to provide
> a good integration between the client and the remote ThinLinc system.
This is likely not a problem however since these facts will probably stay true.