Firstly, regarding the use of ID over Username, the reason for ID being the preferred method is that it is a constant for a Twitch account, where as username can change over time. Some endpoints work with both username and ID’s, some just one or the other.
Next, before searching forums for an answer your first point of call should be the docs https://dev.twitch.tv/docs and the reason I mention this is because you seem to be mixing and matching parameters from different endpoints which is just leading to your confusion and why you’re not getting the results you intend.
For example you’re trying to use the v5 channel videos endpoint as documented here: https://dev.twitch.tv/docs/v5/reference/channels/#get-channel-videos but you’re using ?login= which is not a even valid parameter for that endpoint, furthermore you’re using it half way in the URL, querystring parameters should be at the end of the URL. You should be using https://api.twitch.tv/kraken/channels/<channel ID>/videos or the new Helix api endpoint https://api.twitch.tv/helix/videos which accepts the user_id param (as documented here: https://dev.twitch.tv/docs/api/reference/#get-videos)