V02max based on running rather than cycling, I don't run.

Maybe you don't have a valid VO2max for biking anymore. So it's switching to VO2max based on everyday HR. As far as I recognized it, it will name this "running" even its not from running.

Cycling v02max is definitely there, in Garmin connect I only have a blue graph no green at all. At least three data points a week as well so plenty of data.

There is a priority and the watch uses the latest highest priority VO2 Max value it finds as the main VO2 Max while keeping track of running and biking VO2 Max. If no running or VO2 max is calculated within a 30 day period, the watch defaults to walking or even to “whole day HR” VO2 max.

In your case, it appears the watch found a qualifying activity as a run.

Maybe an activity was mistakingly recorded as a run?

You need to use a power meter to have cycling VO2max.

Already said i use power indoors and cycle indoors at least 3 times a week.

Zero run activities on my account going back years. Last walk activity was over two months ago.

As of the 24th July its back to cycling, still kind of annoying that its constantly giving me information on running when i dont run and never have.

When you look at the VO2 Max curves on the watch under training status, do you see some data points for running VO2 max?

As Etupes25 wrote, there is a priority, and the watch will pick from the Cycling and Running the VO₂max value that it considers more accurate. And as AgentMax noted, values from any non-cycling activities, including the all-day (non-activity) events update the Running VO₂max.

The priority is as follows (from My Recorded Activity Did Not Update the VO2 Max Estimate | Garmin Support)

1. Running Activity With GPS 
2. Walking Activity With GPS
3. Walking Activity Without GPS (i.e. without recording an activity)
4. Running Activity Without GPS

And since you tell, you do not run, the "Running" VO₂max must be coming from walking (either recorded as activity or just plain walking while wearing the watch). Why that value takes the priority over the Cycling VO₂max is beyond my knowledge, but I often see the cycling VO₂max values being a little bit too high, so perhaps Garmin does not trust their Cycling VO₂max algorithm as much as the other types.