Is RoboHelp 2019 compatible with Windows 11?

This old page indicates it is not but as @Amebr has said, you may find it is fine.

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My site www.grainge.org includes many free Authoring and RoboHelp resources that may be of help.

Oh, they removed RH2019 from the list. 😕😕

Here's the cached page: https://web.archive.org/web/20220813040713/https://helpx.adobe.com/robohelp/using/rh_system_requirements.html

Having said that, while it isn't officially tested (or supported) according to that page, it may work fine.

https://helpx.adobe.com/robohelp/using/rh_system_requirements.html