S9+ issues with os kindly help

[Kollervelli]

I got a used Samsung s9+ but I have a lot of issues. The model is SM-N975f/ds which is for note 10+ everytime I set it up with Google, the response I get is your Samsung note 10+ blah blah blah. while the android version is 11 and 11 is not shown on the android 11 version logo. I don't know if it's snapdragon or exynos. I am unable to share files from my computer.
I realise the phone was root with magisk but I don't know how to unroot it and make it go back to factory rom. Kindly help me

 

[DzbanCban]

I think I know what custom ROM you're running, you should have an Exynos (however please check what CPU do you have with an app from Google Play Store) and download stock firmware for your model. Then just flash it through Odin and lock the bootloader if you'd like that.
Here's what models of this phone exist:
European model (Exynos): SM-G965F
American model (Snapdragon): SM-G965U
Canadian model (Snapdragon): SM-G965W
Brazil or Chinese model (Snapdragon): SM-G9650

 

[Kollervelli]

I think I know what custom ROM you're running, you should have an Exynos (however please check what CPU do you have with an app from Google Play Store) and download stock firmware for your model. Then just flash it through Odin and lock the bootloader if you'd like that.
Here's what models of this phone exist:
European model (Exynos): SM-G965F
American model (Snapdragon): SM-G965U
Canadian model (Snapdragon): SM-G965W
Brazil or Chinese model (Snapdragon): SM-G9650

What app should I download from app store pls?

 

[DzbanCban]

What app should I download from app store pls?

Try CPU-Z

 

[Kollervelli]

Try CPU-Z

Thanks
Also will it have any effect if I don't install the oem stock firmware?

 

[DzbanCban]

Thanks
Also will it have any effect if I don't install the oem stock firmware?

The only effect I see is not having official firmware and being rooted (which does not pass SafetyNet).