sapino

Please read full message, before doing anything, thanks.

Close Safari, hold the SHIFT key/button on keyboard, start Safari with double-clicking on its icon.

In this way, Safari starts in SAFE-MODE,

in safe-mode, all earlier tabs WILL NOT BE OPENED/LOADED,

so in this way, you can create new tabs inside Safari,

BUT you will LOOSE ALL EARLIER TABS, in safe-mode.

Alternative:

there are other extension for safari, that can show list of existing tabs & edit (remove) them, ... use one of those to remove the tab that goes into specific webpage all the time.

also see:

Change your homepage in Safari on Mac - Apple Support

Change Tabs preferences in Safari on Mac - Apple Support

Sounds like you installed some type of adware. Check to see if it is a Safari Extension and remove it.

Otherwise, EtreCheck can help you find and remove it.