You've posted in the s9 / s9+ boards but mention the s8 in your post.
Can you confirm which model you have please ?
You mention “ secret menu ” is this via dialing *#0*# in your phone app ? What happens when you do the tests in there if this is the case.
Have you tried the diagnostic tool in your Samsung Members App.
May I also assume no in-transit packaging or case maybe causing this.
If everything you've tried is not working then due to how long you've owned the phone I'd suggest to have it replaced by the business you purchased it from within any relevant Cooling Off Period.
I wish you all the best with this.
Current Phone ~
Samsung Note 20 Ultra 5G SM-N9860_256Gb SnapDragon 865+
Samsung One Ui 3.1/ Android 11.