Sensitivity Labeling will get a more detail External Sharing option in connection to Sensitivity Labeling. In the following you see the option, which will come in this year into Sensitivity Labeling.
In the Screenshot you can see that you have more detailed option. Today you can only allow or disable External User in a Microsoft Teams or SharePoint Site. But in the future you will see more option, which you know from SharePoint default sharing options.
Admin Center: MC225614
Test / Experience
This is a huge step in workiung with Externals and Sensitivity Labeling. If this option is avalible you will find here the Test.