I think it's because Samsung accounts consider different browsers as seperate devices. For example, if you sign in through the settings app, Chrome for Android, and Firefox on PC, your account lists 3 "devices".
If you're still worried, feel free to remove all your trusted devices. The only thing that trusting a device does is let you skip two-factor authentication the next time you sign in on that device/browser. So the only consequence of removing trusted devices would be the mild inconvenience of having to type an extra 6 digits if you ever sign out and back in to your account.
I have EXACT same issue '4 Unknown Trusted Devices' which DON'T require verification and NOWHERE can I SIMPLY see what they are. If I could I'd probably be ok with it but NOT being able to find em?!? Not Acceptable! They should be listed BESIDE that notification of their existence. I've spent HOURS on the Samsung Account/Cloud App and online. Every 3 min if i hit BACK it'll request new log in for TWO STEP VERIFICATION that CAN'T be turned off! Whole thing is EXTREMELY TEDIOUS and poorly designed, filled with features nobody uses and void of most fundamental! Wanna see WHAT'S IN your SamsungCloud BEFORE having to download ENTIRE folders instead of SINGLE files? GOOD LUCK! I took these and other ? 's to a Verizon AND Sprint store..BOTH had multiple employees just as confused as I, TWO employees even remarking:
"We Don't Use Samsung Phones Account Features PERSONALLY BECAUSE of Unnecessary Steps*AND DON'T CALL THEIR CUSTOMER SERVICE CUZ YOU'LL JUST GET CONFUSED FURTHER"
(*THAT! was unfortunate to hear from employees SELLING Samsung products).