There are several telecommunications suppliers in Switzerland that offer eSIM services for the Watch 5, as well as for the Watch 3 and 4: Swisscom, Sunrise..... The eSIM can be easily activated via the app with a QR code.

So I can NOT install an e-sim. Because Switzerland cannot be selected as a location at all (not listed). If it were listed as a location and you could select it, the standard providers should work, BUT it does NOT, or not yet.