Unity: How can I run Unity builds created in High Sierra & Verify they run on Mojave without a Mojave computer?
Since it is tagged with Catalina too, GitHub has machines where a build can be tested.
Just write some automated tests that run using the binary (which you might want to upload to git-lfs) and use GitHub actions to run them remotely.

https://docs.github.com/en/actions
https://docs.github.com/en/github/managing-large-files

There are plenty of workflow files available if you search properly. https://github.com/search/advanced
There might be other such CI/CD delivery options too with other macOS versions.

https://en.wikipedia.org/wiki/Comparison_of_continuous_integration_software