Change SSD, Lexar one is dramless, no point buying dramless ssd at that price.
WD750SN on Amazon USA at $80 SGD cheaper, faster and better with DRAM. Amazon refund policy is a breeze so don't worry about dead drives.
For B450 boards, they don't support Ryzen 5000 out of the box, store need to flash bios for you. You need a Ryzen 3000 and below to flash it.
With regards to Asrock, better google the how the bios look like, some features are not there compared to other brands. Since you going for matx, its either Asrock Steel Legend M or MSI Mortar Max, both are the same price, can google how their bios look like.