Are perimeter insulation boards glued or dowelled in the ground area?

Vertical orientation seems absurd to me, and bonding is a non-invasive connection method, whereby the layer closest to the terrain surface is usually preferably fastened with two methods for safety. Nothing is as perfectly flat as in the textbook; longer panels are merely stiffer, thus less favorable for their adhesion to the surface. I would clearly prefer horizontal installation, with stepped joints and bonded. But as always, my mantra applies here as well: do not let the practitioners use the method they have the least experience with, even if it would be "objectively" more advantageous. Processing influences the overall product "quality" more than the pure material properties or installation methods.

How would you lay the insulation boards? I read "Horizontal, stair tread + glued".
Glued = With thick coating? Only the back or also the stair groove + after gluing the transitions between the individual boards?

So, without gluing the step joint, but only after the insulation boards have been installed, only the transitions?

Don't forget that I have a theoretical profession and two left hands before you follow my recipe 100%. Apart from that: yes, I would set the panels into a flat adhesive bed, leave the stepped joints dry, and later tape all around the joints with strips.