As part of Box Drive's move to a new architecture on macOS (leveraging Apple's File Provider Extensions), Custom Mount Location will no longer be a supported feature on macOS due to an architectural limitation.
We'd like to learn from you your use cases for Custom Mount Location so that we can better understand the impact of this feature change and explore options to consider for the future that could help meet your needs.
For more details on the Custom Mount Location feature, please see our community page:
https://support.box.com/hc/en-us/articles/360043697454-Configuring-the-Default-Box-Drive-Folder-Location