If you are looking for addons whether it's for Shadowlands, Battle for Azeroth, Legion, Warlords of Draenor, and older clients use these two sites:
https://www.wowace.com/
https://wow.curseforge.com/ https://firestorm-servers.com/en/addons/index
At these three sites, you can sort addon projects by what type you are looking for (i.e. bag addons or ui addons). Once you have found the addon you want, you can sort it by patch version.
If you have anymore questions about how to use these sites, feel free to post your questions below.
Happy gaming,
GM Boomkinbear