I have room on iCloud but not on my Mac, how to free up space on Mac

if you are running low on space, you can purchase an external HDD or SSD of sufficient capacity and move your larger files (videos, pictures, documents, etc...) to it. once they are on the EHD, you can simply erase the same files from your internal drive. and, if it's just going to be used for storage, you can use an HDD and save a few bucks over the cost of an SSD. FWIW, i personally keep very little on my internal drive.

also, you may want to read these two articles:

Optimize storage space on your Mac

How to free up storage space on your Mac

additionally, you want to keep ~ 20% of your local drive as free space for proper operation of macOS.

Go to  > System Settings > Storage. You will be given options to store files in iCloud as well as freeing up space by deleting Applications and Documents.

I strongly recommend NOT using any cleaner apps or software that claims to speed it up.