In theory, in 24GB VRAM cards, only the 3090 is possible since it has 24x1GB GDDR6X chips, so if you change the chips to 2GB each, you would have 48GB GDDR6X.
3090Ti and 4090 has 12x2GB GDDR6X chips on the front pcb.
Not sure if 3-4GB GDDR6X chips exist (I think not)
In theory, in 24GB VRAM cards, only the 3090 is possible since it has 24x1GB GDDR6X chips, so if you change the chips to 2GB each, you would have 48GB GDDR6X.
3090Ti and 4090 has 12x2GB GDDR6X chips on the front pcb.
Not sure if 3-4GB GDDR6X chips exist (I think not)