This is an issue on the Venu SQ (and other watches as I have found out)! It is unfortunate that Garmin disregarded this as an issue on other posts. Here is my engineer/athlete's perspective:
Overview: XC Skiing or cold weather running requires wearing a jacket/gloves/mittens. Said jacket/gloves/mittens becomes wet with sweat or elements. To prevent jacket from exiting workouts, etc, I have watch set to auto lock touchscreen on activities to prevent clothing interference. When the watch is locked and touchscreen is touched, the fullscreen lock icon appears for an excruciatingly long time (does it ever go away before the watch face turns off??). This means that whenever my jacket touches the watch during an activity, my watch shows the fullscreen lock icon. This also means that if I move my jacket or gloves out of the way to see the watch I am also greeted with, you guessed it, a large lock icon!! Note this also occasionally happens in warm weather running when sweat falls on the watch face.
Problem: When I am running or skiing, I want to quickly look at my pace or heart rate. As the watch keeps showing me this fullsize lock icon, I get to see neither. If I wait long enough and get lucky, I may get to see my pace and heart rate, but most of the time I don't. I am typically just greeted with a big yellow lock icon. I subsequently yell at my watch, curse Garmin's engineers, and have to make a split second decision to either:
A: Wait and hope my pace or heart rate will become visible, at which time I have probably lost my pace and increased my heartrate in frustration of this stupid "feature".
B: Don't bother looking at my watch during my workout as I know I probably won't get to see the information I want to see (but rather get to see a lock icon I don't want to see), which defeats part of the reason for having the thing!!
Solution (for Garmin, not end user): Put a small lock icon in the corner of the watch display or small banner on top or bottom when locked, allowing everything else on the screen to be seen but also indicate to the user that the watch touchscreen is locked. There is no reason the whole display is needed to show it is locked. I already know it is locked! I either set the setting away from default to lock during activity or I manually locked the display!
ADDITIONAL NOTES (before a Garmin rep completely dismisses my post with PR approved non-response): My household utilizes two (2) Garmin Venu SQ, one (1) Garmin Venu SQ Music, one (1) Garmin Forerunner, and one (1) Garmin Vivoactive. I have been in the Garmin ecosystem since around 2011. We also have a plethora of Garmin bike sensors, Garmin bike computers, and Garmin Tacx trainer. I work as an Electrical Engineer developing automation systems and HMIs for various clients and am an active athlete.
Also note that I just about returned a watch (started the return process with Garmin phone rep) due to "random" auto-restarting in the middle of activities (blue triangle of death). I have since discovered it was due to clothing or sweat activating random functions on the watch touchscreen and at time even restarting the watch through menus. This is the reason I enabled touchscreen locking on my watch during activities in the first place.