This problem existed the past year, but it was finally solved on a february update. Sadly, after some updates it came again, but it wasn't that annoying, but after the 1.16.20 and the 1.16.40 (the most recent) it became terrible.

The problem itself is this: when you use a Nintendo account with +1GB (1.8 GB out of the 500 Mb default, in my case) saved data in Minecraft, the game takes A LOT OF TIME loading the start (before getting in the menu). Loading lapses in my case are of ~8 minutes on a black screen, and almost 20 on the red mojang screen (30 minutes, and I've heard about worse cases). Plus, when you finally load it, the game usually crashes while playing.

Steps to reproduce:

1.Use an account with a good amount of saved data, +1 GB.

2. Start the game and you should notice the long wait.

What is ideal for us: to have the game waiting time that we had before the updates, not  longer than 2 minutes in the worst cases.

I'VE TRIED:

1.REINSTALLING THE GAME.

2.SAVING THE DATA ON THE CLOUD AND RELOADING IT.

3.LOOKING FOR CORRUPTED DATA (EVERYTHING IS OK).

4.CREATING A COPY OF MY WORLDS BEFORE DELETING THEM.

TEMPORARY SOLUTION: the issue gets solved when you save your data on the Nintendo Switch cloud but delete it on the console. It's fine for a week but we've had this for a long time and de aren't able to play on our worlds. That proves that the problem happens most of the times on accounts with +1GB. With the last update (releaded today) the problem persists, And sometimes the game crashes when it was almost loading.

Thanks for reading, I hope this report works.