Why do you think it is a malicious system update?
Thats directly from your device manufacturer website.
Do you think Samsung is deliberately infecting their own devices?

 

i agree with @Dannydet that samsung firmware updates are not malicious. maybe some of them might be annoying as apps can take a while to catch up to the latest updates and thus might not work properly.....but they are not malicious.

here check this out:
https://www.online-tech-tips.com/smartphones/how-to-downgrade-your-android-phone-to-an-older-os/

 

We may be better able to help you if you can tel us why you think that this update was bogus.

Tell us what behavior your device is exhibiting that makes you believe that the update was malicious.

 

It's unlikely that any malware could infect system files in Android 10 on an unrooted device - the sort of exploits that used to be used for that were closed years ago (the reason why all of those "one click root" tools stopped working - they used the same exploits that the malware did). So if you've done a reset that probably covers it, as long as you don't reinstall it (e.g. restoring a backup that includes the malware).

If you want to be safe, go to Sammobile.com and download the latest firmware for your model and reflash the phone. I'm not a Samsung user so can't give a step-by-step for that, but I'm sure Sammobile can. Reinstalling the stock firmware will overwrite your system files, so any modifications will be toasted.

 

that is not possible. in order for that to happen, your phone would have to be rooted to gain access to your system files and be able to read and write to the partition where the os is on......so unless your phone is rooted, this cannot happen.

 

you can just do a factory reset from within your phone's settings. or you can do a hard reset:https://www.hardreset.info/devices/samsung/samsung-galaxy-a01/