Any ideas on how to host a simple html page on routeros.
Need it for government compliance, but do not want to have to pay for a seperate linux vm.

all i can think is replacing the hotspot login page or kind of that

Get a raspberry pi and put it on the network.

all i can think is replacing the hotspot login page or kind of that

Can you do that?

yes, you can use hotspot server for that, to serve static webpage.
You only have to enable it on selected interface where it should listen to requests and then modify/add required html pages.
It's all described in the wiki...

I know the hotspot function can do it,
But I cannot see on the wiki how to set it up as a simple webserver. I want to put it on the public facing internet interface, It is the only non vpn interface on the router.

It is a VM in a datacenter with a single ethernet interface., I cannot simply enable the hotspot interface on the public interface as it will take the mikrotik offline?

There is no webserver in ROS, only hotspot. That's it. Either figure out how to (ab)use it for your purpose or find some completely different solution outside of ROS.

I'd use slightly different description, there's webserver in RouterOS and it could easily handle hosting few user files, but currently no such use is supported, except for hotspot. But the whole webserver is already there, and it would require only few tiny changes to allow this, so it wouldn't be bad thing, because sometimes it could be useful for something.

Until that happens, I'd try to configure hotspot on some unused interface (empty bridge for example) and redirect traffic to its webserver from elsewhere. I didn't try it, but it could work.