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.
This can be applied to many websites. Google and Meta tag tracking data into nearly every link they bring you for popular sites, namely any shopping site. They’re boasting how many clicks they garnered for a merchant while obviously building your massive online profile.
In Google’s case, there’s also massive finder’s fee fraud for ads. I search a specific few products to research them but don’t buy any. I now get ads all the time for them. I then buy one a week later. Google says to the seller they brought me there and takes a commission. All those borderline-unavoidable tracking tags have tied anl served ad I don’t remember to a product I was going to buy anyway