Restore split view with its own set of tabs from 18.12.3
Konsole release 18.12.3 was the last version featuring tabs that may be configured independently for each split view. Any version that followed appears to have a different management for tabs.
Currently, each tab governs each set of split views, disallowing sharing them between tabs (or at least as easily as in 18.12.3). Previously each split view shared the existing console sessions in tabs. Any tab change was limited to the split view only. That was logical, in contrast to the incoherent style for tab management now, where each tab governs its own set of split views. Closing a tab closes all of the split views that it controls rather than only the current session.
Please enable the former mode for tabs as a configuration option. I've been stuck with 18.12.3 due to it being the last version where tabs worked for me.