Currently, the only somewhat complete Blender plugin is "MSFS2Blender" created by Vitus, but the last time it was updated was in September of last year, and lacks some key features and functionality, according to our developers/modelers who have used it here at FBW.
One of our developers has been hard at work for several months on a completely new, open-source plugin which aims to be a complete suite for taking full advantage of MSFS's GLTF spec, and supports importing as well as exporting. Although the exporting functionality is still incomplete, users have mentioned it as having an implementation that is "powerful and more complete." However, our developer no longer have the time to work on it for the forseeable future, and it is difficult to find someone with the specific skillset and knowledge to pick up on their work.
We would appreciate if there could be an official import/export plugin, whether from scratch or picking up on this work (which is open source under the Apache license). Although 3DS Max may be useful for some people, its cost is VERY prohibitive to most people, and dissuades hobbyists and freeware developers for producing for MSFS. Blender is free, and another industry standard.
Here is the link to the repo: https://github.com/flybywiresim/msfs2blender2msfs