It's not going to support the 5.x operational modes, you usually walk the parts into the mode both sides can support from the 1-bit 400 KHz starting point. You probe the CSD and EXTCSD to determine capacities, modes, etc. My expectation is that you'd run out of bandwidth on the STM32 long before you find the limit of the memory IC.
The eMMC BGA have a standard form factor, you should be able to find SD / MicroSD card adapters and clam-shell sockets to verify/validate use of specific parts.
Samsung, SanDisk, Toshiba, Kingston, and others work in fixturing I've done with other STM32, spanning into H7's
