Old story I’m afraid. I’ve never had an XC90 leak but XC60s must use the same windscreen adhesive as Ford (being the Ford years it makes sense), stand beside the A-post & a gentle push in the top corner from below will show most screens move.
The remedy is to either remove & reglue the screen (risking a broken screen) or simply slice out the top gasket & use windscreen glue along the top gap & down the sides up against the decorative trim.
The big hassle is removing the interior - you need to remove all seats, the three carpet pieces, suck out the water but you’ll never dry out the foam so just rip it off the carpet back & replace with loads of house carpet underlay or old towels (the height of professionalism). Replace carpets after drying out on the Mrs’s radiator.
FOR OBVIOUS REASONS THIS IS EXACTLY THE SAME PROCEDURE AS FOR FORD KUGAS, although they also piss in on the body seams under the roof rails & ESPECIALLY those body seams you can see when the boot is open.
ALSO, for Ford Focuses see the italicised writing in the paragraph above.
If I sound like an old hand at this it’s because I am - through bitter experience.