It seems that you have the same error as reported here:
Cant open Sentinel 2 in SNAP 9.0.0 - s2tbx - STEP Forum (esa.int)
Try to update SNAP by using the plugin manager. You can find it under Tools / Plugins.
Afterwards close SNAP, delete the C:\Users<user>\ .snap\auxdata\gdal folder and restart SNAP. Try to open the S2 product again.