If this is the Sangoma provided module you should install it using “make menuselect”. If you don’t, then simply copying the codec_opus.so file is insufficient. The instructions provide further detail on how to install it manually.
If you are using the codec provided by Sangoma then there is a README[1]. There is no configuration of codecs.conf generally required, but you have to copy TWO files into the correct places otherwise codec_opus.so will fail to load.
Otherwise you go into “make menuselect”, Codecs, and choose codec_opus, and then install Asterisk. This automatically downloads and installs it.