Teased in flashbacks to the takeover of Thay and moments in which Sofina discusses her nefarious plans, Szass Tam is the powerful Red Wizard that Edgin and his associates still have to bring down in a sequel movie.

Source: https://screenrant.com/dungeons-dragons-2-story-villain-setup-explained/

This will allow them to break in, steal the tablet and bring Zia back, but while Simon does attune to the helmet (as his Aumar ancestor once wore the helmet), Forge and his Red Wizard in Sofina anticipated the break-in and laid a trap.

Source: https://www.cbr.com/dungeons-and-dragons-honor-among-thieves-kira-darvis-magical-powerhouse/