I think part of OP's problem is that they aren't yet aware of all the sub-skills that go into writing. It's understandably hard to figure out practice excercises when you aren't sure what you should be practicing towards.
Unlike with art, there isn't an organized consensus about them and accepted practice excercises. I've consumed a lot of writing theory and advice content in my life, so I'll do my best to try and make a list of possible excercises based on stuff I learned as well as my own judgement for useful skills.
The most important thing to remember is that writing is the art of communicating your intent. A lot of writing is just figuring out ways to get across the experience you want to create, and so a lot of the excercises are about learning to do that in different ways.
Start out with picking random things and describing them in writing. This is mostly to get used to translating sensory experiences into verbal descriptions. Try describing experiences or things that aren't visual too.
Pick an object. Describe it three different times. Each time you're not allowed to use any of the previous descriptions.
Pick an object. Describe it three different times. Each time create a different connotation for it (an easy trio to start with is good/bad/neutral).
Go people watching. Pick something that's happening in front of you and describe it three different ways. Each time in a different genre.
Play taboo. Describe an object, action or an emotion without naming it or using closely associated words.
Play storytelling Mao. Write a scene where the world and characters act according to a weird and arbitrary rule but never explain it directly or indirectly. Try to communicate the rule with only the character's actions, dialogue and environmental storytelling.
Write a scene with conflict and a twist, then analyze it to figure out what information the audience must know in order to to understand what's going on. Rewrite the scene as a mystery, each time omitting one of those pieces of information and framing it as the answer to the scene. This is mostly to practice awareness of what information you're giving the audience and how its presence or lack of it changes things.
Write a scene with an unreliable narrator. The narrator's perception of what's happening is completely mistaken, but the audience must still be able to understand the truth of what's actually going on.
Write a story with a beginning, middle and end without any dialogue or actions. Use only descriptions to create environmental storytelling.
Pick an object. Describe it three different times. Each time try to evoke a different emotion.
Write a scene with only dialogue.
Write a conversation where the characters never state what they actually mean.
Pick an emotion. Write as many one line dialogues as you can that convey the character is feeling that emotion.
Write a scene with multiple people using only dialogue. You can't state any of the characters' names, yet each speaker should be distinct.
Write a piece of exposition for a character to deliver and have a few different characters say it. Analyze how the character's backstory, culture, status, worldview and personality would change the delivery. What parts would they emphasize and what would get downplayed? How would they frame the information? What's their opinion on it? Would they deliver it factually or insert their opinion? How would their mood change the way they deliver the exposition?
Write poetry (and look up excercises for those as unfortunately I'm not familiar enough to give any).
Write a 1k story. Then rewrite it to be less than 500 words while still telling the same story.
Write a two sentence story. Write a three sentence story. Write a five sentence story. Compare them and analyze the things the extra length allowed you to do.
Look up story structures. Pick a story and try to map it to said story structures. (A good place to start is Snyder's save the cat structure and hollywood movies. Most of them use that structure as template).
Write a story using only sentences with 3-4 words. Then do it with 6-7 words, and then with 10-11 words. Read those stories aloud and analyze the differences between how they sound and feel.
Go people watching. Pick something that's happening in front of you and describe it in three different ways. Each time add a different twist in the end. What different setup did each twist need?
Write the same story in five sentences, then in three, then in two. What had to remain in order for the story to be the same? What was lost? In what ways did it change the resulting story?
Pick a story and read/watch it all the way through. Then go back and analyze each scene seperately. In what way did the scene contribute to the story?
Use a random word generator. Pick one word for theme, two words for plot and three words for characters. Figure out a way to write a coherent story that includes all of them. This one can be changed with any number of words for any category. The important thing is that there would be enough words you need to use that it acts as a constraint rather than a freeform prompt
Write a scene. Then rewrite it so that it starts as late as you can make it and ends as early as it can.
Look up character arc structures. Pick a story and try to map it to a fitting character arc.
Practice debate. Pick a topic and write as many different viewpoints on it as you can. Try to give each viewpoint strong arguments to support it.
Pick a character. Figure out what plot would challenge them the most and what antagonist would cause them the most trouble.
Pick a character and decide on one trait of theirs. Write a foil character to highlight said trait.
Pick a couple of characters and have them argue. The argument can't be stated directly in any way and instead must be communicated through metaphor.
Write a story where the surface story is completely different than the story told when reading between the lines.