The case seems to be one of these, SSD trays shown at 7:05 ...
https://www.youtube.com/watch?v=bYYj_k5qXkQ
I don't think you could squeeze a Pi into the window facing tray, as that doesn't look tall enough, but the trays on top of the PSU could perhaps be modified. I'd personally put it in a concealed HDD tray (8:43) or in the back (13:09).
However you do it I suspect it's going to be a DIY job, and maybe a design it yourself task.
Because I use cases which don't have windows on the sides, can't be seen into, I don't have to worry about aesthetics. I simply bolt add-ons into my PC cases using extension bars or L-brackets and place them wherever they fit. Pi's can bolt onto plastic plates which bolt to the trays, bar or bracket, float in free space. Plastic kitchen chopping boards make suitable baseplates using a junior hacksaw.
A couple of hoops of 'knicker elastic' has held my 3.5" HDD in my 5.25" tray for a good few years now. Perfect acoustic isolation for when the disk rattles
That might work for a Pi too, but it depends on what connects to it. Having sockets and connectors on multiple edges can make that a PITA.