That is strange, I just downloaded Gravel Vertigo and installed it without any problem .
Down loaded Modmanfx latest version today and used it to install Airbus H 135.
I followed the instructions exactly as mentioned in the readme file came with the down load .
every thin went fine and I have the files of Airbus H 135 in community folder of MSFS 2020.
The problem is when I started the game , the Aircraft is not available any where.
any one had the same problem or can explain what went wrong ?