When Tabby terminal is opened it opens by default with 1 Window and can be created N tabs, if that window is closed with the x icon (there is no other way – perhaps some plugin to install? – pls let me know)
If later Tabby is re-opened it opens the same window with its respective tabs. So far all ok. It is configured at:
Settings
Terminal
Startup
Restore terminal tabs on app start (on)
How to accomplish the same goal but for N Windows? Do your own experiment with 2 Windows at least