Files on my iCloud are 2TB. My new MacBook is 256Gb. If I decide to sync with iCloud it fills up my whole MacBook drive. Are there any solutions to only sync specific folders from iCloud so I can have some room on my Mac?
I know there is "optimize storage" on iPhone (not an ideal solution), but is there anything similar for macOS? Or a third-party app that allows me to select which folders to sync.
Apple has posted many suggestions for managing storage space on your Mac at Free up storage space on your Mac - Apple Support
Your problem is that you want to sync, and have only the capacity to sync, a small selection of files on iCloud when the system is designed to unify your content across all devices, even if you have only one device.
Having content on a place where you don't want to access them regularly rather suggests that they are of secondary importance and you might want to consider putting them on a local external drive - and also have two backup copies.
To answer your question about syncing specific folders with iCloud, your Mac can sync three places with iCloud: iCloud Drive, Desktop, and Documents.
Syncing iCloud Drive can be turned on or off. If you have it on you then can choose to sync with Desktop and Documents folder. These two are paired, so you can have both or neither.
To switch the control for these two options go to System Preferences > Apple ID > iCloud Drive
If you put a tick in the iCloud Drive box you can also choose the further option of Desktop & Document Folders. This switch is accessed by using the Options button then Desktop & Document Folders.
Disable syncing to iCloud (only certain folders)
