Nope, vram does not stack, e.g. 2 + 2 is still only 2 recognised. Also many games are not crossfire supported, and possibly needing a new higher Watts PSU, you would do better buying a newer single 4GB/8GB card.
You would need to supply system specs INFORMATION REQUIRED WHEN POSTING A QUESTION for someone to offer suggestions of a possible suitable choice.
Ryzen 5 5600x, B550 aorus pro ac, Hyper 212 black, 2 x 16gb F4-3600c16dgtzn kit, NM790 2TB, Nitro+RX6900XT, RM850, Win.10 Pro., LC27G55T..