I am hoping this was just a joke! But there is so much COVID misinformation out there I feel compelled to respond.
Yes, I suppose if you sent a card to someone who lived somewhere where mail takes less than 72 hours to arrive from where you send it, there is a very small possibility that there is a very small amount of COVID virus on it. This is true whether you licked the stamp or handled the card without gloves.
Because your postal carrier may also be unkonwingly infected by COVID, if you want to be extremely sure there is no infectious virus on the mail you are handling you should keep the mail isolated so that at least 3 days goes by between when the last person touches it (or licks the stamp) and when you touch it.
I know of absolutely no known cases of COVID being transmitted through licked stamps (or postal mail).
Postcrossing is a wonderful, SAFE thing to do during this crisis, licked stamps or not!