The fix that seems to have worked for me is adding a delay between the time I opened a file on a file share and the time I dropped it/created the file in Sharepoint. Also, I didn't notice this issue with small size files. However, when the file seems large enough, the 'sharing' exception occurs.
There is no "Delay" or "Sleep" action in cloud flows (yet). Instead, you can achieve the same thing by adding a "Do Until" operation and increment a counter variable within the loop. Doing addition up to 200 seems to take about 20seconds. So that was good enough for me. Your mileage may vary.
Here's a another helpful article that gave me the hint.
SharePoint 2019 - 'Document Locked for Shared Use by [Me]' - Microsoft Q&A
Hopefully MSFT puts a fix to this odd behavior.
Good luck.