Minecraft W.I.P Memory Map Attempt 2.0

This is the 2nd attempt at a map I've made.

This has been something worked on at various times.
At the time of this video, I created a fourth world to try and work on it.

The only reason I made this video is I needed the space and I hadn't worked on this in a bit.

Some details:
Started out just trying to make the general direction. Due to not having the best understanding of command blocks, I tend to keep the commands near the scene of the action so to speak.
Ironically in the process of trying to find commands for the boss, accidentally found someone who had done videos on datapacks. I had had no intention of really getting into that, but through watching the videos I began attempting an almost hybrid attempt with the maps.
Hence the functions.
However, where I really got stuck was the boss. I have tried multiple times to get the bossbar to work, even following almost line by line tutorial, but it never has worked properly. Either it shows, but doesn't update, or it doesn't show at all.
The summon works, though.
Unfortunately I also do not have enough knowledge yet on how to create the ai for the boss, which is the other reason I stopped for some time.

For the same reason I made this video I am also doing the 3rd iteration attempt.