Start by picking up trash/things that should be thrown out. You don't need to put them in the trash can, a cardboard box or a foil bag that you can put closer to you will do. Or just stack them all in one place.
Then move onto the "putting things in their places" part. Lastly into vacuming and washing and stuff. For me personally it's less overwhelming when I divide cleaning into these "stages" because I don't need to switch tasks so often (or at least my brain perceives it that way??)
You don't need to do it all at once, it can be done over hours, days or weeks. Whatever works for you. Also if you're stuck on something specific, like it feels especially hard to do (for me it's always putting clothes in the wardrobe) you can skip it and move onto something that feels easier. Or just half-ass it. Doesn't have to be perfect, better to do anything than nothing.
If you have many things that you're not sure where to put, get some kind of box/basket and just throw them in there so you can at least free up some space. Mostly works for small things though.
Just.. remember there's no shame in not doing everything perfectly. Your room doesn't have to be all pretty and shining, start with just making it functional for you.
Find ways in your daily life to make a bit less mess. It can be quite hard, but maybe you can work out something that doesn't require you much energy, but saves the future you from cleaning. For example when I cook (which doesn't happen often though lol) I put all the leftovers/trash on one plate and then throw it all out in the end. Easier than leaving a mess on the counter for the future me.
