2nd movement of this Sonatina 3 bars before Figure E in the Novello edition (Bar 30 in any other edition) it has in semiquavers
Bb
rest
Gb
Eb
Gb
Eb
Gb
Eb
Gb crotchet tied

How should the Gb be fingered? Only the thumb or 12 only?

You could try thumb only. That works for me, though it depends on the recorder I suppose.

Yuhuh It's much easier to use the thumb only fingering to alternate with the E flat

I'd agree with that - having just had to do the same with F#-D# in a couple of the pieces I'm trying to learn. I do find it takes my brain a while to learn to do that at speed, because I'm so used to connecting the dots on the page to the other fingerings...