Filtering for GP's requirements on GSMArena.com, I only see a handful of recent phones. Some of them do have an unlockable bootloader, but all of those are made by GPL violators, so you won't get the source code necessary to really make use of that unlocked status.

EDIT: I forgot to check the "removable battery" checkbox; with it you get zero matching phones. Maybe you should've checked that before assuming GP just can't search.

Not to end on such a negative note, foregoing a maimum height and the removable battery, Sony's Xperia 5 and 10 fit the rest of the requirements and are very good phones. Hard to find for sale in the last few years, though.

hehe so just kinda made Perfect non existent product. free niche :)