The next version of WinSCP will shorten the tab titles to always fit all tabs to the window:
Bug 1423 – Better handling of large number of tabs
The solution you've implemented in v6 is awful – there were original requests to wrap the tabs over multiple lines, not to make them truncated so much as to be unreadable!
Please make the shortening and truncation of tab names a configurable option at the least please.
If only one row is possible for you, adding mouse wheel scrolling like VS Code and Notepad++ would be a huge bonus over just arrows.
I signed up purely to vote for the fix for this.