I have recently started flying MSFS2020 and I was interested in this topic. I found this:
Simulator weather cannot be shown for MSFS since SimConnect weather functions are deprecated and do not deliver data. Use NOAA weather which gives you the most up-to-date weather reports.
Source: 66.3.2. Microsoft Flight Simulator 2020
https://www.littlenavmap.org/manuals/littlenavmap/release/2.6/en/APPENDIX.html#microsoft-flight-simulator-2020