Ticket is here, not sure exactly when it'll be fixed, we'll try: https://github.com/bryntum/support/issues/4189
Support Forum
Hi @Animal, for compatibility testing we use this service https://www.browserstack.com/, here you can select the OS and browser version combination, when we select MAC (OSx Monterrey and Safari 15.1) the issue appears ... but if we downgrade to MAC (OSx Big Sur and Safari 14) everything it's OK ...
Regards