Exposed concrete/grout in shower where the door slides between the frame and tiles, possibly too large to caulk

The house that we bought has a shower with sloped tiles on either side of the shower tray. The door is a sliding door that slides into a gap between the tile and the door frame. The gap that the door slides into is concrete and/or grout. I need to seal it before we can use the shower but I don't have any experience in caulking/sealing gaps like this. From what I've read this gap might be too large to caulk, if so are there any recommendations for how I should deal with this gap and seal it correctly while leaving enough space for the door to slide in and out.

Measurements:

Side 1, slope is at a 10 degree angle, deepest part of the gap is 2.5cm.

Side 2, slope is at a 14 degree angle, deepest part of the gap is 4.2cm.

If any other detail would be helpful, let me know and I'll try my best to provide it.