It seems to me that you've never changed a chain yourself.
Let me recommend another video. In my opinion, he explains it best for laymen and is a likeable guy:
https://www.youtube.com/watchImportant: If the chain is already too long, it will have worn out the chainrings and sprockets. Then it won't be fun with the new chain. A chain gauge is therefore a must-have. You can say that a new chain needs to be fitted every 2000 kilometres. This prevents the lengthened chain from grinding out the sprockets/chainrings too much. If you miss this point, it's better to stay on the old chain and ride down the sprockets/chainrings. If the chain starts to jump over the sprockets, you'll have to replace everything. Then it can be dangerous.