Please share more information, as the feature does work. Remember, the recipient may choose to ignore it and the recipient's email provider may also choose to ignore it. Requesting a return receipt is not related to global settings. You can request a return receipt from the Options menu when the global settings is turned off.

Thank you David - there's not much more I can add. I'm using Thunderbird 115.9.0 and am fully aware that a return receipt can be chosen from the Options menu when composing a message. However, this has not worked for some time. I also use Proton for certain jobs and the Send Receipt option there works!