Your computer's free disk space and your Google account allowance are different totals. Check where the warning appears. Changing Drive's sync settings can reduce local storage use without reducing what you store in Google.
You bought more Google storage, but your laptop still says its disk is nearly full. Or you cleared your Downloads folder, but Drive still refuses an upload. These are different problems, even when the same files are involved.
Read the warning in the place it appears
A storage warning in your computer's system settings points to the disk in that device. A Google account storage warning points to the online allowance. Take a screenshot or write down the exact message before changing anything.
Check both totals separately. It is possible for one to have plenty of room while the other is full. Keep the two numbers in separate notes so you can see which action changes which total.
Understand what Drive for desktop is keeping locally
Drive for desktop offers streaming and mirroring. Mirroring keeps a full local copy as well as the cloud copy. Streaming mainly keeps files online, while files in use or made available offline can still use local space. Neither option increases your Google allowance.
For a laptop you usually use online, streaming may be worth considering. For work you need without an internet connection, plan which files must stay available offline. Choose based on how you use the device, rather than switching settings just to make a warning disappear.
Source: Google Help
Do not delete a synced folder to experiment
Changes to synced files can be reflected across devices. Follow Google's documented steps when changing from mirroring to streaming, and wait for syncing to finish before removing old local copies.
If you are not sure whether a folder is still syncing, stop and check that first. A folder that looks like a spare copy may be the working location used by an application. Open a few important files from their intended location before cleaning up the old one.
If the online allowance is the problem
Review your Google storage breakdown, then the largest files in Drive. FreeUp can make supported Drive files smaller, which reduces the space those files occupy online. It is not a laptop disk cleaner, and you should not assume an immediate matching change in a local cache.
If the computer is the only problem, deal with local downloads, applications, and sync settings instead. If both are full, work on them separately and verify each result. That makes it much easier to avoid repeating changes that solved the wrong problem.