When you store a file using iCloud, Google Drive, DropBox, Box, etc... the file is actually local on your hard disk. Software running in the background will occasionally copy the file up to the cloud server. The issue is if some other computer is also connected to the cloud and someone is making changes on the two different machines simultaneously. The background software that is uploading to the cloud will just make a copy if it finds the two different machines both changed the file.
QuickBooks Mac 2019 has code that detects if the file is being changed by these background processes. If it is QuickBooks will ask you which version to keep. This means its possible to use the cloud software and keep your changes as long as you aren't using the file on two machines at the same time.
Note that the cloud software also has to finish updating the machines... it still takes some time to copy the file up to the server and back down to the second machine. For instance if you make a change on one machine but then walk out of wifi range the copy to the cloud may not occur.
So there you go - you can with 2019. iCloud is what we designed it for as iCloud has additional APIs and (I think) also works while the machine is asleep and plugged in. But it should work with other services, too.