The link below contains a table that includes your panel. A footnote to the table says that you can use the THQP 1/2" breakers.
NOTE: Actual number of circuits may be increased to maximum UL allowance by utilizing GE’s exclusive 1/2” THQP circuit breakers. See carton labels or Residential Product Catalog (DET-222) for details.
Is the flex conduit the full size conduit, or is it armored cable (Type AC)? They look similar except for size. You can't pull new wires if it is armored cable rather than flexible metal conduit.
NEC 250.118(5)(c.) permits the flexible metal conduit to be used for the ground only up to 6 ft in length. Armored cable can be used for the ground if it is properly terminated in metal boxes.