The page https://openwrt.org/toh/mikrotik/common contraditcs itslef.
OpenWrt is not compatible with the bootloader of RouterOS v7 or v6.46 or above. Do NOT upgrade the firmware on your device past RouterOS v6.45.8 or, if you did, downgrade to RouterOS Firmware v6.45.8 or earlier before installing OpenWrt.
Yet the section on how to do this says:
bootloader from RouterOS v7 is not compatible with OpenWrt … downgrade to RouterOS v6 …
If the version is below 7, you are all set. If it is 7.*, downgrade RouterOS to v6 before proceeding.
Which is it?
I tried to downgrade as per openwrt instructions:
[admin@RouterOS] > /system routerboard print
routerboard: yes
board-name: hAP ac lite
model: RB952Ui-5ac2nD
revision: r2
firmware-type: qca9531L
factory-firmware: 6.48.6
current-firmware: 6.48.6
upgrade-firmware: 6.45.8
It suggest I won't get the bootloader to 6.45.x, whilst:
[admin@RouterOS] > /system resource print
uptime: 5m16s
version: 6.45.7 (stable)
build-time: Oct/24/2019 08:44:35
factory-software: 6.44.5
free-memory: 30.5MiB
total-memory: 64.0MiB
cpu: MIPS 24Kc V7.4
cpu-count: 1
cpu-frequency: 650MHz
cpu-load: 1%
free-hdd-space: 3476.0KiB
total-hdd-space: 16.0MiB
write-sect-since-reboot: 137
write-sect-total: 27276
bad-blocks: 0%
architecture-name: mipsbe
board-name: hAP ac lite
platform: MikroTik
indicates the factory software to be 6.44.x
Totally confused 
I'd like to get openwrt on RB952Ui-5ac2nD (hAP ac lite)
Thanks!