Using BetterSnapTool, the drag-to-snap no longer works in Outlook since upgrading to macOS Catalina. It seems to be drag-to-snap alone that's not working. I can re-size Outlook using the window position/size menus, and by using keyboard shortcuts. Other apps work for all three methods.
This is with BetterSnapTool 1.9 and Outlook 16.29 (19090802), macOS 10.15 (19A583) on a 15"MBP, A1990.
unfortunately outlook is one of the apps BetterSnapTool will need screen recording permissions for. For now you can add BetterSnapTool manually in system preferences-> security & privacy-> privacy -> screen recording. There will be an update that explicitly requests this permission next week.
also see screen recording??
Here is a beta of BetterSnapTool 1.9.1 which should ask for the new Catalina screen recording permission and work better even if you don't grant it:
Would be great if you'd test it.