Can I safely remove scratches from Apple Watch face using toothpaste?

I think the key word is safely. There is nothing safe about putting toothpaste on a touch sensitive surface and expecting to rub hard enough to remove a scratch and yet do no further damage. Jewelers have polishing wheels to remove minor imperfections that are much less abrasive than toothpaste and will still tell you they are not responsible for any damage it may cause to your Rolex or other expensive watch. Remember those watches have crystal watch faces and no touchscreen capability.

Bottom line, as long as your willing to self insure for any damage you cause and understand the cost of replacing the touchscreen, I say go for it. After all, it its your Apple Watch.

Maybe. But you will possibly damage the water-resistant seals in the watch in the process. This may permanently damage the watch and it can no longer function.

M1 Mac mini, macOS 14.5;  Watch, series 7 GPS/cellular, watchOS 10.5; iPhone 12 Pro, iOS 17.5; TV 4th Gen, tvOS 17.5; HomePods, audioOS 17.5 and Airport Express w/ Airplay 2

I won't go hunting down the section now but typically Apple has wording in its legal documentation that they will not perform repairs or honor warranties to devices that have undergone unauthorized modifications. In other words, if you try toothpaste and Apple detects you have done that it might give them reason to not honor a warranty or outright deny any repair service of any kind on the Watch. Generally it is best to play it safe until you are sure Apple will never look at the Watch anyway (beyond service life) or you just don't care.

We are end users like you, Apple is our hosts however they don’t read or participate in these forums. It’s your watch you can do as you please however be prepared for consequences if you decide to move forward with your idea.

Let us know what you decided to do!

You’re welcome. My old Rolex has scratches, I consider them more like scars from a life well lived.

I hope you have a great day.

Look at the bright side. His Watch will have fewer cavities.