Sounds like you are keeping the company file on a disk on a remote computer and mounting that disk on the local machine where you are running QuickBooks. That has never been a supported approach - the reason is that it can lead to data damage. This is due to the use of a network file system (usually SMB on modern MacOSs). The network file systems don't support file locking correctly in many cases.
What you should do instead is run the QuickBooks Server on the remote computer and then serve the QB file from that. Other machines in your internal network can then connect to the served up company file. This should be faster but more importantly it is safer.
A single license allows any of the remote computers to connect to the file as long as no two connect at the same time (it will actively block that). Whereas in the situation you have now two users _could_ connect at the same time which can also lead to data corruption. If you need two users to work simultaneously you need only buy another license (or another copy of QB Mac 2019).