The part that says either ?si= or &si= is only for tracking. You can remove this part of the link and it will still function just the same. It makes the link shorter and also helps protect your privacy. The only important part of a YouTube URL is the video ID. There are two types of URLs:
For this one you can remove everything after and including the ampersand if present.
For this one you can remove everything after and including the question mark.
Note the exception is if you want to intentionally leave in playlist information you might want to keep that part.
For any android users reading this, urlcheck can auto remove tracking portions if a link, as well as allow to automatically apply the link to a privacy focused front end (is that what e.g. nitter is called?).
Sure it’s still am extra step to share the link to urlcheck first before sharing it to your recipient. But hey it takes out the menial task by a lot.