The AC devices are still able to run legacy wireless even with most recent ROS v7. Follow these steps:
- download extras archive for architecture ARM and exactly right ROS version running on your hAP ac2 from https://mikrotik.com/download
- open archive and extract wireless .npk
- upload file to your hAP ac2
- go to System -> Packages and mark wifi-qcom-ac for uninstallation
- reboot device
After these steps verify that wifi driver package was indeed replaced by wireless.
After this is done, your device will not have default config for wireless applied. You can either work through it manually (I suggest to go with this option) or reset to factory defaults (and rework any specifics you may have now). It might be possible to do something about wireless config by going through quickset but this will likely mess with the rest of (customized) config so I advise against it (unless you perform factory reset before that in which case quickset won't have anything to mess with).