Recently migrated from the Note 8 to a Note 10 Plus using the SmartSwitch app:
-- Google Clock app, NO dismiss/snooze icon on lock screen when alarm fires!
-- Tried adjusting setting within the app and the lock screen settings, nothing!
Let's start from scratch:
-- Goto: Settings > Apps > Clock > 1. Force Stop; 2. Storage; 3. Clear cache; 4. Clear data.
-- Exit all apps.
-- Launch the Google Clock app, set a test alarm, lock the screen.
-- Wow, that worked. Whew!
-- Likely cause, Google Clock stored data from the Note 8 wasn't compatible with Note 10 Plus.
-- Solution, clear all cached and stored data, restart the Google Clock app.