steering wheel vibration only when the engine is warm

my car is a 16′ BMW 750i (G12) with 26,000 miles on it currently.

When I first start the car, there is absolutely zero vibration at all, but I’m starting to get a vibration only through the steering wheel when I’m idling at a complete stop.

I did some testing, and the vibration is produced either…

5 minutes of normal driving

OR

20 minutes of idling

…after I cold start the car. So I’m guessing that it is something related to the engine temperature?

I thought it would be something related to an engine oil level (I recently changed oil at a private shop), but the level was perfectly in the normal range.

So then, I thought it would be related to some mounts, but I only have 26K miles on it, and why would it vibrate only when the engine is warm? If the mounts are bad, shouldn’t it vibrate every time or even worse when it is cold?

Could it be some cooling system like a water pump or radiator fan working when the certain engine temperature is met? But when I turn on the A/C which I believe activates the radiator fan, there is still no vibration at all if the engine is not hot.

I have been searching for this over a month now, but no luck. I recently visited a BMW dealer, but the service advisor said this is in the normal range (which I definitely think is not. It feels almost like a weak cellphone vibration), so I couldn’t even get a diagnostic. Any suggestions or opinions on this problem? Thanks