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I would suggest doing a Factory Reset so any setting added will be removed. Find how to do this here: https://www.samsung.com/uk/support/mobile-devices/how-do-i-perform-factory-reset-on-my-mobile-device...
I had the exact same issue. Fixed it from settings,lock screen, always on display, clock style.
Hope the answer helps. I had to dig deeper as I had a lot of info transferred from the old phone.