I want to use an addon that works with MEP 2018-2021. The 2022 MEP is free with the latest Autocad. But can I also use it if I install Autocad 2021? As far as I know, MEP 2021 was not free.
MEP is a separate software, not an add-on, never has been an add-on, never will be an add-on.
Anyone with a current subscription can get MEP as a separate download in versions 2022-2021-2020 and 2019.