The different ways of adding a theme

I don’t see any further questions on your previous thread asking for clarification?

It works as simply as I stated:

theme = "github.com/user/repo"

This assumes your site is a hugo module. So you would do beforehand:

hugo mod init "your-mod-name"

As to why you couldn’t get it to work, I wouldn’t know. Refer to Requesting Help to see what information you would need to provide for us to be able to help.