BIOS Update / Flashing

Updating your BIOS can be *very* dangerous. Don't touch a working system; a bad BIOS flashing can result in a computer not rebooting.
If something goes wrong with the BIOS update, be very careful. You can repair the motherboard by removing the BIOS chip and replacing it with a new one.
You must never remove the plastic around the BIOS chip. *Only* the BIOS chip. If you remove the plastic it'll be next to impossible to replace it and your motherboard will become junk.

Motherboard issues

The ASUS ROG Strix Z590-I motherboard is quite fragile. If it refuses to boot, often the issue can be fixed by removing one of the RAM memory sticks. It will then boot, and you can put back the stick right after that. Note that the yellow (orange) light on the motherboard will often be lit up if there is an issue with the RAM. Such issues usually happen after any hardware modification (switching from Intel built-in GPU to a external nvidia one, unplugging the computer and moving it, etc).
Make all hardware modifications with this motherboard with the computer turned off (it's very important!), and even better, with the power cable removed from the computer.
This motherboard had a built-in backplate (for the CPU cooler or AiO pump) on the back of the motherboard. It's not tightly screwed and can feel like it's loose, it's normal. It's holding only via the other side of the motherboard, the front side, when you screw the pads needed for the cooler.

Once I had an Asus motherboard (ROG Strix Z590-I model) that suddenly refused to boot. Clearing the CMOS (check the manual to know how to do that) fixed the issue.

Motherboards usually come with their own I/O panel - a metal shield that should be put at the end of the computer case. To fix it, push it from the inside of the motherboards while applying pressure simultaneously at all 4 angles.
Motherboards don't contain a lot of cables - those come from either the power supply block or the case itself (cables are needed to link the USB ports in the front of the case for instance).

Be very careful - do not bend the motherboard in any way! Never. Some of the holes in the motherboard may align with holes in the case where there is not any preinstalled "brass standoffs". In that case, you must first install those brass standoffs, and only then attempt to place your motherboard on those brass standoffs.

Mini-ITX motherboards are great for SFF (Small Form Factor) PCs. Be careful about the external power supply adapter that those boards need; they usually require a 7.4 outer diameter coaxial cable. That's the case of the Asus Pro H410T.