There are two parts to consider when answering this question:
Part 1: MIMO As A Method
Multiple-Input Multiple-Output(MIMO) is the ability of a wireless communication system, to exploit multipath propagation by multiplying the transmission and receiving antennas on the radio link, to maximize the data rates. Both WiFi6e and 5G systems can use MIMO.
Part 2: 4×4 MIMO On A Technology
5G can achieve data rates of up to 1Gbps, while WiFi6e can realize data rates of up to 9.6Gbps. This is because the highest modulation that can be implemented on 5G is only 256QAM, while on WiFi6e it can go up to 1024QAM.
With the two considerations above, it is then noted that as a method, MIMO is the same on the two wireless communication systems, but when implemented it can differ depending on especially the modulation scheme implemented on each system.