Writer's Block or Something Else?

So I know where I want to go in my book, I know how it should end. I know how it should tie up. I even wrote the ending. I just don't know how to extend this book. I don't think I am very good at subplots. I took a break to write my "Star of Zephyria" Book simply because I didn't know how to extend it. I was advised to watch other things, things I like to see what they did as subplots. To see how some books I loved had subplots. I read several books, I don't remember the subplots. The books I do remember the subplots, I don't remember the main plot. I was also advised to just write random stuff. I'm building a world, make it a world. It's in third-person anyways. I don't have to stay with the main characters. It helped a bit but I'm still struggling. While struggling, I have started on other books...books I know I won't dedicate a lot of time to because it's just a tool my brain wants as a distraction from what I feel like is an impending doom. What should have already been finished because I'm 40k+ words done, is now taking me longer. If it continues past my deadline for myself, I will turn it into a short story. I know it's a cop out but right now, I don't know what else to do. We will see what happens in the next few days.

Also! I am watching "Falling into your Smile" Super cute C-drama, highly recommend...I may be watching it a second time but who cares. I love it. Also something I did this last weekend, I went to the movies on a kinda double date with my husband, brother and sister in law. Also nephew but he's a cute kid. S0 we went to the new Demon Slayer Movie...don't watch if you are caught up on the show. Do watch if you are halfway through the last season of the Swordsmith Arc. Then you'll be okay. I was half way so I was happy. My brother's family...not so much. It was all recap minus 40 minutes of it.

Anyways, that's what I am up to. I probably should start recording these ramblings but it's hard to do since I will continue to ramble and that's not fun.