Problems installing plugins

Hi, I tried to download and install a plugin called geckolib, but it won't let me use any of the plugin, I also tried to go to the workspace settings to the external apis section and the plugin doesn't appear either, and that when I install it, from the program or entering the plugins folder, it tells me that it has been added correctly. I tried to install others and the same thing happens to me.
If someone could help me I would appreciate it.
All the best.