Hello @Yndigo ,
Welcome to Microsoft Q&A forum.
I have helped to report your feedback(improving and adding the documentation about Run Test With -> Custom Parameters feature).
Currently, you may try to use command line tool(integrated terminal in VS for Mac) and command line/parameters to specify and use a .runsettings file.
There’s a similar ticket: .runsettings file with VS Mac and NUnit 3 VS Adapter for you to refer to, and a similar reported ticket(under review): How to select runsettings file in Visual Studio 2019 for Mac, please kindly follow up, add comments and vote for the ticket. You can also directly report the issue to product team by submitting a new ticket on our Developer Community - VS for Mac.
Thanks for helping us make Visual Studio for Mac better, have a great day.
Sincerely,
Tianyu
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