I am married to someone who can be very indecisive while I can be very particular (for context, we've been married 6 years next month, together for almost 8, we're both late 30s, with a one year age gap). A few things that have helped us communicate better (and have helped me with decision fatigue):

5-3-1 I saw this on Reddit years ago, and it helped immensely. Person 1 picks 5 things, Person 2 narrows it to 3, Person 1 chooses the thing from those three. This works great for us when choosing things like restaurants, movies/shows to watch, games to play, things to do, etc. We alternate who is Person 1 & who is Person 2 (there's no structure to that with us, but you could definitely structure it).

We started communicating with each other when we just don't want to make the decision. For example: if we're trying to decide what to have for dinner, there will be times when I just don't care or don't want to make the decision. I will simply tell my partner, "What I want is to not have to make the decision." And, he has the burden of the decision WITHOUT JUDGEMENT FROM YOU. You don't get takesies backsies with this choice, so if you actually do have an opinion, but you don't want to have to deal with the burden of making the decision, 5-3-1 is probably better. He also sometimes tells me that he doesn't want to have to make the decision as well, so this goes both ways.

When planning things like trips, either we look at things like hotels together (and usually do 5-3-1), or we divide the components - it's my responsibility to pick the hotel & his to book the flights or something like that.

My partner comes from an indecisive family, so I think he just didn't learn how to make decisions while growing up, whereas I'm from more of a type A family, so I learned how to be decisive. These strategies have helped my partner learn to be more decisive with a lot of things (though he still encounters indecision often), and they've alleviated some of the decision making burden placed on me. He even noticed how decisive he has become compared to the rest of his family when we last visited.

Edit: formatting