Whoever was fidding in the panel last really didn't know what they were
Whoever was last doing electrical work on this panel probably shouldn't be invited to return for more, given what they managed to screw up with your shop circuit. Your GE panel, instead of using tandem breakers (2 breaker mechanisms in a single pole frame) for "double-stuffing" the panel, uses a half-width breaker frame instead, and your panel is indeed loaded mostly with THQP half-width breakers.
This is fine as long as you're dealing with 120V circuits; however, a 240V circuit requires two breaker poles that land on adjacent bus stabs. For full-width breakers like the 90A subpanel breaker in the bottom-right, this is trivial. However, half-width two-pole breakers like the ones used for the two 20A circuits for your shop require a bit of care to ensure that they end up straddling two bus stabs, as the breaker for the working circuit is doing, instead of being crammed onto a single bus stab in the fashion that was done for the breaker feeding your broken circuit.
GE CTL panels such as yours, furthermore, have a rejection feature in them that should prevent the last installer from doing what they did. As a result, either your faulty 240V circuit was fed by a pair of handle-tied single-pole half-width breakers (which the rejection feature can't stop from being mis-inserted), or the installer must have done something sketchy to get the breaker to fit where it didn't belong.
So, I would ask the electrician to pack a couple of THQP120s, a TQLFP1, and a THQP220, and have them move the faulty 240V circuit over to the bottom-left of the panel between the two existing 20A 120V circuits there, replacing the existing 20A breakers in the process. They then can plug the hole left by removing the old breaker with said filler plate since we don't know if that bus stab's even usable any longer after potentially being abused by the prior installer.