Thanks.
I think the problems with Corsair RAM and Ryzen chips is overblown. And since you tried Kingston too, it would not be that. But your issue could still be RAM so I would try one stick at a time.
Since this problem happened with 2 different graphics cards, it is probably save to assume it is not that.
Power is always suspect, even with a brand new power supplies so if me, I would swap in another known good supply and see what happens. Hopefully you have a spare or a family or friend you can borrow from.
Note that cases are designed to support 1000s of different motherboards of different sizes. So, it is common for cases to have more motherboard mounting points than some boards have mounting holes.
A common mistake by the less experienced and distracted pros alike is to insert one or more extra
standoff in the case under the motherboard. Any extra standoff creates the potential for an electrical “short” in one or more circuits. The results range from "nothing" (everything works perfectly) to a wide assortment of odd problems, to "nothing" (as in nothing works at all

). To add to the confusion, these issues may be intermittent, depending on heat, expansion/contraction of materials, as well as continuity/resistance through the contact point. Therefore, you need to ensure the case only has an inserted standoff where there is a corresponding motherboard mounting hole.
Note the latest version of the ATX Form Factor standard hopes to eliminate these issues by dictating where standoffs
will go, not just where they
may go. But not all existing boards or cases comply with those latest standards - yet. So, you still should verify you only inserted a standoff where there is a corresponding motherboard mounting hole.
So I recommend taking everything out of the case and assembling the computer on a large, unfinished bread/cutting board to see if it boots there. Then inspect the case and verify again, only the necessary standoffs have been installed in the correct places before reassembling back inside the case.