Many users have reported problems resizing Legacy. When you attempt to resize the window it rebounds back to what it was.
To fix this turn off the Windows 10 Appearance & Performance Option setting "Show window contents while dragging" as shown in the screenshot below.
Click Windows "Start" at bottom left on your toolbar and begin typing Appearance.
Click "Adjust the appearance and performance of Windows"
Go to tab "Visual Effects" and turn off "Show window contents while dragging"
In Legacy customization 10.1 Screen Fonts set:
"Stretch fonts when resizing" to ON.
We have also had users report that if you close the database but not Legacy (file>close file in Legacy) it reduces the number of redraws and thus reduces the problem with resizing. To do this do the following steps:
From the File menu, choose "Close File" to close the currently open family file; the Legacy program stays running
Resize the window as desired
Reopen the desired family file
If you are using Windows 11, here is an article that may help fix this problem: