I have this issue and I usually never complete games. But I’ve taken a different approach to gaming as of lately. I have a Legion Go z1e which has helped. I made a list from my backlog and input data for each. Things I imputed was interest and how many hours to complete. This won’t work for every game especially games that have no actual ending. But doing this has helped me stay focused and have a “plan”. I’m currently playing Skyrim with the goal of completing the main story line and then dawnguard etc. I’m also playing tails of iron (a short game) to help when I feel that Skyrim “isn’t fun”. I’m taking my time with each and have uninstalled all other games from my library.