Marc I use Microsoft Edge's tab groups in its layout with horizontal tabs a lot! They're very useful!
In Edge, I often use windows as groups of both stand-alone individual tabs and tab groups. The ability to have multiple tab groups (and other, ungrouped tabs) in the same window is quite nifty. Admittedly, I guess this is kind of like having some sets of nested tabs each buried only one level deep? You can use tab groups with the horizontal tab layout, though.
See also: https://orionfeedback.org/d/79-tab-folders