If you're running Sonoma your MB Air must be from 2018 at the oldest, so you can't add RAM. Reducing running programs might be the solution. Some possible ways to help:
1) Go to System Settings/General/Login Items. "Login Items" are programs that automatically run when you login. If a program were necessary for your computer to run it wouldn't be here - these are for your convenience. Delete any you don't want. Some programs may insert themselves here when you set them up.
Also in this window: Allow in the Background. Apps may be performing tasks in the background, eating up your RAM. As with Login Items, these are not required, so you can turn them off if you wish.
2) You probably know this, but on a Mac, if you just close an app's windows, it will still be running. Press Command-Tab to see the apps currently running. Holding down the Command button and pressing Tab again allows you to move between apps, so you can quit any of them. (Command-Q or from the app's menu bar).
3) If an app doesn't want to quit, you should be able to use Force Quit. It is available under the Apple menu, or by pressing Command-Option-Esc.
4) Were you reading your RAM usage from Activity Monitor? If not, you can find it in this folder: Macintosh HD/Applications/Utilities. In the top row of the window (see below) you can select which aspect to view (CPU, Memory, etc). In the next row if you select Memory it will sort by the amount of RAM each process uses. There should also be a column for User (which I hid in this image for privacy), which is usually either you or the system. You can shut down a "process" from Activity Monitor, but that's a little advanced for me. I just use it to see if there's an app that is hogging the RAM, and shut things down from one of the ways above.
I hope this is helpful.
