Since 2024/3/07, the running data from Garmin to marathon world no longer includes running metrics such as cadence, heart rate, temperature, and humidity.
Since some of the data is transfered it means that they are connected.
Do you see the missing data in Garmin Connect?
I've created an account and some of my training has been imported. I see heart rate, but not the other data.
One odd thing that I see is that it says "TCX 2.0 Upload". Why isn't it using the FIT files. If I download the TCX from Marathon's World I get a TCX with lots of data missing compared to the data in the TCX by Garmin. If it is using TCX files then it is understandable that data is missing since those files don't contain all data.
I believe Marathon's World is doing something wrong. I suggest you file a support case to them.
I'm using the web for my tests: https://www.marathonsworld.com/artapp/login.php