Frequency on "auto"?! No possibility to say what you are getting. (No control over channels used and as such no control over the TX power)
Check "status" on WLAN interface and "registration" in wireless.
Signal strength, obtained 'interface speed/bandwidth/# ofstreams/guard interval'.
With strength better than -55dBm, Interface speed should be 300 Mbps, dual stream, SGI. Throughput should be around 100 Mbps then, unidirectional.
(The wAP can do triple stream, but this also fully depends on the client, which mostly can't.)
For 300Bbps throughput you will need 866Mbps interface speed. Better than -45dBm signal strength, 80 MHz bandwidth, dual stream, SGI, .... and the UAC AP switched off (with any other interferer)
Security can only be WPA2/AES (no TKIP!) for these speeds.
I checked my config via unifi controller and I have it set to 40MHz for 5Ghz and 20Mhz for 2.4GHz but I disabled the 2.4GHz network on it and I didn't setup 2.4GHz on the Mikrotik.
Ran the speedtests with the unifi unplugged then I unplugged the Tik and ran the test on the Unifi with only it plugged in. I speedtested from my Thinkpad P50 with Intel 8265 nic and on my Samsung Note 10+ which is rated all the way up to 802.11ax support.
Guess I'll do the 80MHz on the Mikrotik.
Oh and I made sure to disable TKIP, only AES WPA2.