You can try Archive of Our Own (AO3). It has a large collection of fanfictions, including many MCU DC crossovers. Just use the search function and type in relevant keywords like 'MCU DC crossover' to find what you're looking for.
A popular one is 'Heroes United'. It's a more light - hearted take on the crossover. Flash and Quicksilver have a friendly race that turns into a mission to stop a time - traveling villain. It's full of humor and great action sequences that show off the speedsters' abilities.
There's also a fanfiction where Thor and Superman are pitted against each other in a friendly competition that turns into a real battle when a powerful villain manipulates the situation. It shows how their powers compare and contrast. Thor's godly powers and Superman's alien abilities make for an interesting dynamic.
I have no idea which DC Comics character you could be. You might need to describe your skills, backstory, or any special abilities you think you have that might match a character from DC Comics.
You should start by creating a concept. Maybe it's a world where the Infinity Stones and the Mother Boxes exist together. Next, plan out how the characters will interact. Will they be friends or foes at first? For instance, if you're crossing Wonder Woman and Thor, think about how their different cultures would play into their relationship. Then just start writing, and don't be afraid to let your creativity flow.
Well, it really depends on what specific qualities or behaviors you exhibit. Maybe if you tell me about your powers, personality, or costume preferences, I could have a better shot at figuring it out.