How to come off beta programme

That's probably something you'd need to ask the company you're recycling it with.

But to leave, you need a computer with the smart switch software installed

Agree with arianwen27 definitely worth checking. I would highly imagine if you are selling it to someone like music magpie etc who will sell the phone on it would likely fail their checks if on beta. Use smartswitch on computer to reinstall latest official. I have posted instructions for several other users so worth checking the forums for my previous posts or Google is your friend 😉

Hello @Jab007,

To withdraw from the One UI Beta Program, you must apply
for withdrawal through Samsung Members application on your
device.

After that - to remove the beta software, perform a rollback to the
previous release version, using the Smart Switch application
on your computer. The rollback resets the device and removes
data generated during beta testing.

If you do not have access to a computer and need to roll back
your device, contact the nearest Samsung Service Center.