Hi, would love to get the ability to open a set (or sets) of grouped tabs upon startup of Brave on desktop. Would be a great quality-of-life feature 
If you have Continue where you left off, Brave should start how you left it when you close it, groups and windows included.
You need to make sure you close the browser by exiting through the menu, not by clicking on the X button in case you have multiple windows, and to make sure all processes get properly closed.
You can enable the flag chrome://flags/#tab-groups-save to easily save and load groups, and easily click the groups you want to save and restore.
There is also a great extension like Tab Groups Extension which will make it easier to load or save groups, and also auto group tabs based on different things like hostname, full URL or page title case sensitive or not.
So you can easily add pages to Open a specific page or set of pages and then use the extension to automatically groups them on start, based on their full URLs which I guess would be the best. So you can create the groups you want that way.
I mean you are asking for a vague feature request, but it can currently be done with a simple extension like that.
The browser is meant to work the way it is supposed to work, this is a feature probably Chromium has to add anyway, unless Brave added a way to auto-group tabs like the extension does.