Openplanet is an extensive modding and scripting platform for Trackmania 2020, Trackmania Turbo and the Maniaplanet games.
It features a wide variety of built-in features and benefits from a community of developers that frequently add new plugins and scripts.
More info here: openplanet.dev
To be able to use any Openplanet plugins, you first need to install Openplanet into your local Trackmania instance.
Check out the official instructions - if you run into any issues, please report them on the official Openplanet Discord server.
There is a wide variety of plugins available, you can find a few highlights in the Openplanet Plugins article.
If you know that a map contains certain custom blocks or items you’d like to use, you should first check if they’re available on ItemExchange (if the map is on TMX you can find a table of custom assets when you scroll down - if they’re on IX, there should be a direct link).
If you can’t find them there, it’s worth trying to just ask the author for them - you can often find them on one of the Trackmania mapping Discord servers.
Only when you are unable to get the blocks/items that way, you can opt for the rather impolite method of just extracting them from the map yourself.
CurrentMap\_EmbeddedFiles/ContentLoaded and click Extract.