Problem with new build PC (Ryzen 5/ASUS Rog Strix)

Did you wipe the affected area of the thermal paste spillage with alcohol while powered off? Thermal paste is electricity conductive. It may short something.

The BIOS does not need updating unless you require a new feature.

I'm not a tech., but I have just completed my first build too; which failed at the first hurdle.

Suggestion: Take out the RAM and reseat it - checking that you are using the correct slots.
Disconnect everything from the motherboard, apart from the motherboard power, CPU power cables and case switches.
If it still fails to fire up, first check that you have the case connections correctly installed.
You have tested with an alternative working power supply so that is OK.
What are you left with? The CPU, CPU fan and the motherboard.
By removing all other items rules them out of your problem solving.
If the motherboard does fire up correctly, replace the connections one at a time to the motherboard, when it is off!
Each time try to boot. If any one of the additional items causes the motherboard to fail to boot, you have identified the problem!
Good luck.
Mine turned out to be a failed power supply, after 10 minutes of running OK! :-(

You did connect the monitor to the graphics card not the motherboard ?

OK, BIG problem. That motherboard only supports the cpu you installed from bios 2301 on. Since that bios was just released two months ago, I highly doubt your board shipped with a compatible bios.
Your choices are as follows;
1 Return the board and go with a 570 chipset motherboard which has native support for the 3xxx series processors
2 Purchase a low end processor so you can update the bios
3 AMD used to have a loaner program where they would loan you a processor to update a bios. Not sure if this is still being done