On other smartwatches I’ve used I’ve been able to lock the screen from touches and button presses until a specific combination of buttons are pressed, or a button is pressed for a duration of time.
Sweat can activate the screen unintentionally during a workout and workout equipment can bump the buttons, ending the workout early. My friends and I all wear smartwatches while we play hockey to track our exercise but if we forget to lock the screen the workout always ends unintentionally within ten minutes because our gloves have accidentally pushed the right buttons to end the workout.
I would suggest a combination of buttons be held for 3 seconds to unlock the screen. Preferably one button on either side of the watch (back + up) or as a less ideal option the up + down buttons be held. The apple watch also uses this unlock sequence to play a noise through the speaker of the watch intending to dispel any sweat or water that found its way in there during the workout. Idk how necessary that is, but might be something to consider.