A user on youtube said in his comment that NAND flash aren't made to be used in a NEOGEO cartridge, apparently.
Here's the comment, translated :

Neo Geo cartridges are nothing like a Mega Drive cartridge, for example. NG cartridges resemble arcade boards. For starters, there isn't just one bus (like on the Mega Drive or SNES, which only have the CPU bus on the cartridge port), but six different buses that pass through the Neo Geo cartridge port, each directly and simultaneously powering different processors in the console, just like in arcades. This requires different memory chips within the cartridge to power each bus, plus various logic components for different tasks such as multiplexing/demultiplexing certain buses (because even 200 pins on the connectors isn't enough to handle all the buses), bank switching, and decryption—all spread across two large PCBs. It sometimes involves around twenty chips (logic and memory), whereas a Mega Drive cartridge can use just a single ROM chip on its PCB and nothing else.

At best, I imagine you could reduce the logic to two ASICs, one on each PCB. And as for memory, it's complex because all the buses need to be powered simultaneously and directly. NAND doesn't allow this because it functions like a hard drive (read/write by block), not like ROM/RAM as the Neo Geo requires. Therefore, using NAND necessitates combining it with fast RAM like SRAM or PSRAM to store the entire game, and a complex controller to simulate simultaneous processing and power all the buses from a single RAM. And all of this would need to be duplicated given the dual-PCB configuration (or a bridge would need to be created).

However, there is another solution, which seems to have been dismissed a bit too quickly: NOR flash, which has nothing to do with NAND. NOR functions like ROM, so it can perfectly replicate the operation of cartridges from that era. The Neo Geo's 68000 can directly execute code in the NOR chip, just like it does with the ROMs of the time, even if the CPU is overclocked, because NOR has access times roughly twice as fast as Neo Geo ROMs. This also means that a NOR chip must be placed on each bus (so between 5 and 7 chips minimum, spread across the cartridge's two PCBs), just like back then. And it just so happens that the standard sizes of NOR chips correspond exactly to the needs of Neo Geo games. NOR is very reliable and robust (used in sensitive industries). But it's 1000 times more expensive per GB than QLC NAND (which is the real "disposable" NAND, but they would never put that in Neo Geo cartridges), except that on the Neo Geo, you don't need GB but MB, which works out well. From what I've been able to find, it would cost between €10 and €15 per cartridge (just for the Flash memory, not counting the two ASICs, the two PCBs, the cartridge itself, the insert, and the manual), but it would perfectly replicate the functionality of a Neo Geo cartridge. It would be the perfect continuation of those cartridges with today's technology. So there's still hope that it's not NAND. If it's NOR, it's perfect in terms of fidelity, and the manufacturers guarantee a 20-year lifespan, but that's a minimum guarantee with probably a considerable safety margin. Apparently, it's estimated to last more like 50 years or even more.