I'm quite surprised that it is an outdated trope, well I guess I could understand what you mean by that. But if you were to say through ‘portals’, it would only be used in a few events of the novel. For other events, he would either suddenly appear in the alternate world or being summoned there...
Hello, I am the author of the novel An unknown world. I am kind of interested in your service for the other authors here, so I would like to send you the link to my novel.
Here is the link:
https://www.scribblehub.com/read/285055-an-unknown-world/chapter/285058/