The file formats seem very similar to Grid 2019. So, I am hoping you can implement support for Grid Legends accordingly.
We've been looking into this. It appears that the custom UDP output feature (present in most current generation Codemasters games) is broken in Grid Legends. We've relayed this to Codemasters and are waiting for a response.
In the interim, we're working on a release that will utilize the old UDP extradata feature, but it won't have the same capability and performance as the version that allows us to custom define the data we want. This is due to the limited data available in the old school UDP output mechanism that we need to use in the interim.
I don't have an exact ETA yet. I spent a fair bit of this weekend beating the custom UDP data dead horse. It'll probably be Monday or Tuesday before we have something running for Grid Legends.
UPDATE 02/28/2022- We released an initial version here: https://www.simxperience.com/downloads
We had to use the old method (ExtraData = 3) used by other vendors rather than the more sophisticated version that we would normally use with other Codemasters games. I apologize for the delays, but it was worth at least trying to use the latest technology. We may be able to utilize the more robust custom UDP version in the future as we continue to work with Codemasters to address the variances between Dirt/F1 and Grid titles.