This is the way to deal with it. As always, if you find anything on the internet that you like and don't want it to change underneath you, you need to make a copy into a space where it cannot change. In the case of Spotify, you need to duplicate the playlist or if you really want it to be permanent, pull down the mp3s from somewhere and have locally, as it can still be pulled from Spotify once their agreements run out.

I thought we all learned this when people started to have 50% of the bookmarks from the 2000s dead by now, but seems we still have generations that need to learn from the precariousness of content on the internet.

Spotify doesn't have something as basic as a "clone playlist" feature, so not really an option for any non-trivial playlists.