"but I don't know where to start"
Lay in grass for 5+ minutes just existing
Look for cool rock/stick to hold for a little bit
Look for shapes in clouds
Kick leaves on sidewalks in autumn
Blow dandelion fluff in summer
Close eyes and listen to birds/nature/weather (recordings are fine)
Drink from a running tap with your hands
If you have a little more time, some more complex activities for your monkey brain:
Get a bag of peanuts and peel them open with your fingers. If you don't eat peanuts/are allergic, try a different nut. If you're allergic to all nuts, get green beans or snap peas and crack them all open to eat the insides first. Sunflower seeds/pumpkin seeds will work as well.
Put some treats in capsules (cheap Easter eggs with great) and hide them around your dwelling. Candy/snacks are fine but stickers or other small rewards work too. Foraging brain will like this. Bonus if you can exchange hiding with a friend.
Go on a walk/ride to a new place. Novelty is essential for mental health. If you're not sure where to go, literally just pull up Google maps or something, zoom in on your location or nearby, and look for a shop you've never been to, then go explore it. My partner just took me to a thrift shop I'd never been to, and my brain will be picking over that new memory for days.
Once in a while, find a restaurant you've never been to and go get something in person even if it's just picking up a dessert. Try to order something you haven't before, or haven't in a while. You might hate it, but that will be an enrichment, too.
Go to where a social event is happening/where other people are. You do not have to participate, personally, but regularly going to where there are humans doing human stuff is immensely beneficial to mental health. Libraries, museums, and parks are a good starting point.
Look up local festivals in nearby towns and look at stuff people made by hand/at home. You don't have to buy anything, you don't have to make anything yourself, but seeing things people made by hand will Do Stuff for your brain, especially if you're stuck in doomscroll brain rot mode. Look at that little lumpy bar of soap, that little hand-knit scrubbie, that frog made out of old utensils. Things are still being made by humans all over, and you can go and look at them in person.
If you have the money, get some cheap canvas (near me Michaels has cheap canvas packs that go on sale for like $2/canvas) or thick paper and some poster paint in your favorite colors, and paint with your hands. It doesn't have to be a picture, just use your hands to smear paint on canvas. Poster paint is generally washable, so if you hate it you can just wash it off. Wear gloves if you need to, but put your handprint on that cave wall.
If you're able, arrange to speak out loud to at least one friend a week. "but I hate-" I know, but it's good for you to speak aloud to other friendly primates and share stories. Story sharing is huge for humans. You don't have to be a writer to tell stories, talk about your trip to the grocery store or the cool rock you found. This will have the bonus effect of starting you looking for things to tell your friend on your phone call, which slows you down and lets you notice your life as it's happening.
You don't have to do everything, but doing some of this, or similar actions, can get you started on treating yourself as the primate your body is. Problem solving, treats, exploration, novelty, socialization, creation, observation, and engaging in your available physical senses are all things your mind and body, as a human, need in order to be enriched.