It has nothing to do with rclone. And is not a bug.
Most likely you have program(s) on your system reading a lot of files. In additions you amplify the problem but not using full cache.
Possible culprits on macOS might be Finder generating files' thumbnails, spotlight indexing etc. Can be also some 3rd party stuff. It is impossible to guess.
rclone on macOS or Linux behaves the same. What is different is software you are using.
Thank you. Any recommendations on reducing API calls other than --vfs-cache-mode ? Does --fast-list and --checksum help? I have seen that being recommended for sync but not sure if it is helpful in the mount setting.
Yes it might help a bit but in your case this is probably not the key issue. If the same mount command on Linux does not generate so many API calls then on macOS it is something else.
Identify what program is reading so much and either not use it or change its settings. For example in Finder you can disable thumbnails generations for the start.
Also maybe do not mount all S3 bucket but only folder you are working on? All depends what it is for.
change --log-level NOTICE to --log-level DEBUG
the rclone debug log will show which apps are accessing the mount and what is being accessed.
the first item is ListBucket, that could be from using a low value for --dir-cache-time
the lower the value, the more api calls.
does not apply to S3 remotes. the debug log would show that.
might use defaults or reduce the chunk size.
does nothing on a mount
might try --vfs-cache-mode=full, then rclone will cache the downloaded chunks and not have to re-download.
have you considered switching to a provider that does not charge for api calls, does not charge for outbound transfer?
given that you are using session token, might consider wasabi for some or all of your data.