Not being an expert on the FWD Volvo's take my advice with a grain of salt.

We noticed some of the behaviors you mentioned on our Saturn race car in the wet many years ago and it caused us to actually go through the all of the mechanicals that affected the guidance of the wheels under braking load. Three things became apparent:

All the bushings in the suspension were completely shot (this is budget racing) but the ones on the driver side had become oval while the passenger side were just soft, cracked, etc.

Springs left to right did NOT have the same free length or sag.

The driver side strut appeared to have considerably less compression damping in the "soft" initial part of the stroke.

How does the apply to your situation? If neither caliper is binding (piston seals still retract the pistons and slide pins still slide) you are looking at differential wear of items that affect Ackermann steering but also squat under braking. These are usually only the bushings at the suspension and steering mounting points. Lower a-arm bushings worn oval will change toe with less force as well (they are designed to change toe, but if the drivers side does more easily...).

Likely, you are looking at soft parts or calipers or a combination of both.