Safari Profiles - New windows open with: Tabs for -profile-

I really hope someone here can help me understand this. The simple task I'm trying to accomplish is when I open a new window for a particular Safari profile, like Work, it should open a few specific tabs, like Google and Apple. I know it's possible, because I somehow set it by accident. Safari's profile settings have this option, to set new windows to open with "Tabs for -profilehere-".

Now, I know this will do what I'm trying to accomplish, because I did it by accident today. When I opened a new window in the Work profile, the three tabs I'd had open earlier in a window were part of it. I couldn't change what those three sites were, and I've tried everything. I've created new tab groups from open tabs, new empty tab groups, new profiles to try recreate it, changing the setting to something else and changing it back to Tabs for Work. Nothing has worked at all.

I've just spent the last 3 hours this morning trying to talk to Apple support about this (first through chat, then over the phone), and I haven't been able to get a simple answer to the question: What are "Tabs for ____" in Profiles settings for Safari, and how are they chosen? One technician had me delete the only profile I'd gotten to open a specific set of tabs for new windows, and I stupidly agreed and now can't even show that it IS possible anymore. Support, in the end, told me that no one I will be able to reach at Apple will be able to give me an answer to this, since all they are trained to do is direct customers to the support articles already available on the website, and my best chance will be to ask the community. I don't feel like I'm asking for the moon just trying to get someone to explain what this setting is and how it works, I kind of feel like I'm going crazy. I've spent weeks before today trying to figure this out, and I really do believe I've read every single article available about Safari profiles. This is seemingly never explained.

If anyone here knows how this works, I'm really at a loss here. I'd be really grateful for any assistance. Thanks.