When I used Outlook together with EMclient, any email action in one app (e.g. delete or saving in a folder) would be replicated in the other app.

I now use EMclient together with Protonmail because at least I can sort by sender in EMclient - which a long overdue feature in Protonmail. But if i delete an email in EMclient its still sits there in Protonmail and is difficult to find amongst the many many pages of emails that have stacked up.
Replication of email actions in one app - Protonmail - needs to be replicated in the other app - in this case EMclient and vv.

To not provide this capability is living is the ages of dinosaurs - move on Protonmail or I will.