If the IMAP is syncing all the time - start with this registry key - Microsoft is investigating an issue where Outlook doesn't close properly when you have an IMAP account in your profile and this can cause Outlook to have sync issues. There is a registry key to use as a workaround. If you don't want to edit the registry, I have a ready-to-use registry file available https://www.slipstick.com/doit/AllowLOGOUT.reg
HKEY_CURRENT_USER\SOFTWARE\Microsoft\Office\16.0\Outlook\IMAP
DWORD: AllowLOGOUTWithoutOK
Value: 1
If you've already set it, do you have any sync issues? Look in the Sync issues folder in the Folder navigation pane (Ctrl+6 to open it if the buttons are on the bottom). If your Outlook navigation buttons are in a vertical bar on the left, click the bottom icon in the vertical bar and choose Folder. (To switch back to the Mail pane, click the Mail button or use the keyboard shortcut Ctrl+1. )
Errors will be in red text in the Sync Issues folder.
One option is to change the IMAP sync settings to only sync the inbox - the other folders will sync when you open them.
Go to Send/Receive settings (Ctrl+Alt+S) - select the send and receive group then click Edit. Uncheck get unread count for subscribed folders. Under received items, set it to only check inbox - you can include sent items if you want, but opening the folder will trigger a sync.
