Took way longer than they should have done, but I’m out of practice.

Long tail cast on 52 stitches, join and work in the round, being careful not to twist.
15 rounds of 2x2 ribbing
15 rounds of stocking stitch before start of thumb increase
Increase 2 stitches every third round until thumb section has 21 stitches.
Put the 21 thumb stitches on holding yarn and continue, backwards loop cast on 4 stitches.
in the following rounds, decrease the newly created stitches back down to 52 stitches in total and continue for 12 rounds
10 rounds of k2 p2 ribbing, stretchy cast off
Pick up thumb stitches from the holding yarn, then pick up 4 stitches against the glove body.
Decrease down to 20 stitches over a few rounds and knit about 5 rounds in total before 5 rounds of k2p2 ribbing, cast off and sew in ends.