just go to coracle.social and check your profile details button on the top right and uncheck the thing that shows the npub so it shows hex

you can also on many clients click on a button that shows the raw JSON of your note and your pubkey appears in it in hex also

hex = 0123456789abcdef base 16 it's the most widely used encoding for binary data since forever

... button on the bottom right on nostrudel has an option to View Raw down the bottom of the menu, then click json and your pubkey hex is in the field "pubkey":"abcdef12134p23456235..."