I have posted elsewhere about setting up imapsync in docker for this for both command-line AND web interface usage. We have used that tool for so long... but one thing I do miss from Plesk is the mail migration tool. This DID make it easier, since you could stay in one interface.
One reason I like/prefer impasync is that we can setup a migration file, and do the mail sync as many times as required to obtain all the emails. This is true for customer email boxes moving onto our servers AND migrations of customers to other platforms such as Outlook, Gmail, Zoho... Set the script, fire off and it just works.
I know that Giles is working toward a web interface that mimics the command-line stuff, where you can setup multiple mailbox migrations at once from the web interface. Now, THAT, will be a game changer for us, because we can use our system, or for customers who are touchy about passwords, spin up a one-off for them to handle the migration...
I do think that a basic IMAPsync-like system in enhance would be awesome.