You're in luck! An update to atmosphere supporting 9.1.0 is about to release very soon, keep refreshing the releases page on the github. You can see in the commits they already implemented 9.1.0 support and bumped the version number to 0.10.0. I believe the reason why it isn't in the release section yet is because they still have to implement support for the other modules atmosphere uses (exosphere, etc.), most likely emummc, or they are currently testing and making sure there are no bugs/typos in the code and that all of atmosphere's functions work properly.