Found this video really interesting as I have a relatively large backlog myself. Fortunately not nearly as large as this one.
Personally, I’ve only ever considered games I own to be part of my backlog, which makes my list much more manageable. That said, I have a large number of unplayed games on both Steam and GoG. So to start I’ve decided to play all my GoG games first (as that is still within reach). I’ve promised myself not to buy any more games untill all my GoG games are either completed or marked “did not finish” due to it not being my thing.
I don’t really get the obsession with backlogs. Are you actually enjoying the games at that point? Are you playing this game because you want to play it, or because it’s on your backlog and you want to be able to check it off the list and move on to the next thing - presumably, since your backlog is so big it warrants a guide - as quickly as possible? Just pick out a game you want to play and play it. Why spoil your own fun?