Modern Mac operating systems use the APFS file system. This file system has a built-in backup feature called "local snapshots". When you delete a file, it will not automatically erase it. Instead, a local snapshot will hold onto the file. Eventually, local snapshots are deleted. When the last local snapshot that has a pointer to your file gets deleted, the spaced used by that file will become free again.
If the operating system starts to run critically low on hard drive space, it will start deleting local snapshots early. This should free up storage space by finally deleting that file. But this process does not happen immediately. You will likely get some disk space warnings first.
To complicate matters, when you check to see how much free storage you have, you may see it referenced in terms of free storage "available". This is not actual free storage. This is a representation of how much storage could be make available, by deleting local snapshots, for example, if the operating system really needed it. You can use Disk Utility to get a more accurate picture of how much actual "free" storage you have.
If you are running low on free storing, you are never going to make any headway by freeing up storage in single-digit increments. 8 GB is nothing. What can you do to free up 80 GB? That's what you need. Turning off WiFi will not help. Please do not use any kind of "cleaner". Those will scramble your system.
You may be able to recover space by deleting more files. Or you could move some files that you rarely need to an external hard drive. Note that Time Machine is a backup system, not an archive. If you delete a file, it will eventually be deleted from your backup too. If you want to save a file forever, you need to archive it to a separate, external hard drive.
Another option would be to purchase Cloud storage and move your files there. For iCloud, all you have to do is turn on iCloud Drive, perhaps enabling Desktop & Documents. Then any file on your Desktop or Documents folders will be automatically moved into iCloud. Eventually, this will result in more free space locally. There are tricks to speed this up, if necessary.