Many 4×4 and 2×2 MIMO antennas support both 5G and 4G, can both be used simultaneously?

It’s not advised to split a 2×2 MIMO antenna over the 4G and 5G ports as this will cause frequency clashes. You can split a 4×4 antenna over 4G and 5G as each 2×2 pairs are isolated within the antenna.