In Samsung Health on my S10+, go to the Steps page. Tap the dots in upper right, view step count data. Tap the All Steps button in the center with the little link icon. Tap on Mobile Phone Only. Once viewing Mobile Phone Only steps, tap the dots in the upper right again, and you should be able to PAUSE MOBILE PHONE STEP TRACKING. Shame that its such a complicated workaround, and difficult to find on ones own.
... View more