I don’t see an issue with microwaving glass jars. The packaging may indicate whether or not it is suitable to microwave. Personally if I was going to, I would turn down the wattage, and heat for longer (heat is distributed more evenly), and definitely mix to avoid any super hot or cold spots. Be sure to remove lid first.

As long as this glass jar is microwave safe tandem sterilised why not

There are no issues that I’m aware of for heating glass jars in the microwave, not like there are with plastic containers

You can heat glass in the microwave but it can create heat spots it will need a good stir. I heat it up in a bowl