From AP-530 Series datasheet, AP-535 supports 5GHz radio 4SS single user (HE80) up to 2.4Gbps or two 2SS HE80 802.11ax MU-MIMO capable device simultaneously.
I used Samsung S10+ that supports 802.11ax 2.4G+5GHz, HE80 for throughputs validating device. The downlink throughputs in the application layer could reach up to 800Mbps. However, as I tried to let the second Samsung S10+ do the same test at the same time. Each of the Samsung S10+ had dropped to 350~400Mbps individually.
I checked the document saying that MU-MIMO is enabled by default. But somehow from my expectation, the AP-535 4X4:4 should provide two 2SS HE80 devices reach the total capacity like 2.4Gbps in the link layer rather than 2 S10+ with total capacity around 800Mbps in the application layer.
Below is the configuration parameter setting for the access-points. Please kindly provide suggestions to enable MU-MIMO function.