Two main choices there.
No pink logo at the bottom means it did not display a valid header.
Dirty pins (which can come from factory or make poor contact with certain combos of device -- had plenty that work in one but not another*). Clean the pins and if you want to fold a bit of paper a few times to put between the PCB and plastic case to force better contact then some go for that too.
*also worth checking if your GBA is one of those with modded screen or something fun as those have caused issued with the more power hungry efforts.
Whatever is supposed to be on the SD card is somehow necessary for it to boot properly. I would not necessarily expect this but it has happened before.
That said I am still at a loss for this. As mentioned above most old school stuff used some combo of NOR memory or NAND memory and RAM. SD cards did appear very late in the day on the GBA with the supercard and GBAMP (some of which were also CF instead) from the same people that did the M3 and G6 and thus technically the first R4 but tended to be in larger form carts than standard GBA. It looks like none of those. By the time of the DS then things started using external memory more but most went for miniSD and then microSD to try to get it to fit more easily, especially when the DS lite soon appeared (until more recent things then the last gen of GBA slot DS flash carts was aiming to be in the DS lite slot).
I am not aware of any homebrew flash carts/designs that used SD memory or were particularly amenable to it, and I would have thought anybody good enough to both injection mould a new shell (that does not look like someone tool a rotary tool to an existing cart) and redesign something in current space year would have used a microSD slot (same cost, less PCB space wasted and it is a cram to do things here).
On 16 gig card I will also note you might need to find a 2 gig effort -- 0 to 2 gigs (with some vanishingly rare non compliant 4 gigs) were SD format, 4 to 32 was SDHC, 64 to I forget was SDXC and there is a newer one still these days. Many devices like this will only work with what they know and that might well be SD only.
To that end you have something very unusual there. I will await PCB shots.