What makes the situation trickier is that both the gattlib undeclaredly depended on here and the alternative pygatt (see #939619) just wrap the gatttool program, which is deprecated by the bluez project (not much info out there, https://github.com/peplin/pygatt/issues/112 gives a good summary).
While making gattlib available in Debian might solve the issue on the short term, it might be worth looking for more current alternatives instead; I don't clearly see one yet though.
