Hello mate!
The Shadow Adept class is only granted if you are Sharran, which gives you the shadowweaving skills.
Previously, people were taking Sharran as a god to get shadow adept class which would grant them shadowweaving, then changing their deity. However, it is Shar who grants you shadow weaving. Shar would not grant you the ability to use her magic if you don't worship her.
Shadowweaving information:
https://forgottenrealms.fandom.com/wiki/Shadow_Weave
The requirements of Shar have always been required to use Shadow Adept, which is also here:
https://bgtscc.fandom.com/wiki/Shadow_A ... quirements , so to originally of gotten it, you would of been Sharran, at least temporarily, but forsaking her as a deity would see her also revoke her granted spells. You can change your deity to Shar to use shadowweaving however, or you would need to RCR.
Shadowweaving was enforced to Sharran only as the class required (Shadow Adept) about half a year ago. Maybe a little longer!
Thanks!