How to turn off stabilization?

I am trying to film video on an iphone with a gimbal mounted on a

bike and have run into problems with unexpected wobbly mush-like effects

that I believe are partly caused by the iphone's native stabiliser

being pushed beyond its built-in tolerance limits, so would like to know

if it is possible to turn the stabilizer off?

Until today my understanding was that (1) native optical

stabilization in recent iphones like the iphone XS is done via a fixed

piece of hardware that cannot be turned off, and (2) native digital

stabilization in legacy iphones like the iphone 5 was built into the

native camera app with no option to turn stabilization off.

But I have become confused about this after reading reviews of

several different paid-for video camera apps that according to the

reviewers include the option to turn stabilization off or on.

Does this mean  the developers of these app have figured out a way to

turn off the inbuilt optical stabilisers in recent iphones, turn off

native digital stabilization in older iphones, or does it just mean that

apps like Filmic Pro just add their own enhanced digital stabilization,

as an additional stabilization effect on top of the native

stabilization built into iphones, that can be switched on or off?

What do you think - is there a way to turn off native stabilization,

either in new or legacy iphones, or is it just a marketing gambit like

hiring a ventriloquist to make a corpse appear to talk?