When you have more than one query to run at the same time from the same SQL Editor, this feature will create multiple different tabs to display each result set separately. TablePlus currently supports up to 100 result tabs.
This option is enabled by default but if you need to change it:
Clicking on the config/setting button at the bottom left of the Query Editor
Select/unselect Split results into Tabs (max 100) to enable/disable it.