That's a little broad and not true. The question mark (and subsequent ampersands) delineate URL parameters, and those are used for a variety of things of which tracking is just one.
Example: YouTube links have the format "youtube.com/watch?v=" followed by a string of numbers and letters. ?v= denotes the parameter for the video ID – the video you want to watch. Without it, you're just linking to YouTube's front page.
Forums, if anyone cares to remember them (from a time before social media rotted everyone's brains) tended to run on PHP, so a lot of the time their links would look like this: "exampleforum.example/showthread.php?thread=1234556789&page=25#reply15". Here, the parameters ?thread= and &page= tell the backend which thread and page to display, and the anchor #reply15 jumps to the fifteenth reply on that page.
Web shops use parameters to store i.e. size, colour, etc., so if you bookmark an item for later and remove these, your link will at best not store the size and colour (or other product variations) you selected and at worst just not work. What's more, Google offers the option to visit a no-AI version of their search page with the parameter ?udm=14 (you're welcome); if people just blindly removed every parameter from every URL (and yes, the query you search for is also a parameter), that wouldn't work too, any more.
Telling people to just strip out every ? and & they see is to breed digital illiteracy and set them up for failure.
Teach them to learn instead. To understand.
Most of the time, it's pretty trivial to understand what things do if you look at them for a moment and think. The aforementioned "showthread.php?thread=12345&page=25#reply15" is fairly self-explanatory once you understand that ? and & are URL parameters and # jumps to a named anchor in the page.
And likewise, ?si= (share ID) and its brethren are not that hard to spot. Anything that has "utm_" in it is Google Analytics. Instagram uses "gsh" as one of its parameters, and occasionally generates "instagram . com/share/(post and user ID go here)" links that uniquely identify you to anyone you send the link to instead of "/post/(post ID)".
Unthinkingly following overly broad instructions doesn't help you. The only self-defence is to understand what is being done to you. The advent of smartphones has alienated and entire generation or two from the idea that you can understand how computers work, but it's vital that you reclaim it.