I recently had a similar issue when I went to trade in my late wife's Galaxy S10 phone. It kept going around in circles, telling me to log in to her Samsung account. I tried updating the password, but that made no difference.
The guidance at https://www.samsung.com/uk/support/mobile-devices/how-do-i-perform-factory-reset-on-my-mobile-device... worked for me. I first removed the Google accounts (I think I had set up her phone originally, and both our google accounts were linked to the phone). Then, after powering down the phone, I held down the volume up, power, and Bixby keys until the Android screen lit up, at which point I released them. It booted in to a screen with tiny writing. I used the volume down key to select the option to do a factory reset and pressed the power key.
I think it then prompted me to reboot the phone. When I next powered it up, it behaved like a brand new phone, so I assume the reboot had worked.
