i have an old version of mac on an old laptop. i want to download an old version of garage band :)

Is the system version given below your question "macOS 10.13" correct? You can see the system version when you click the  menu in the upper left corner of the main menu bar and click on "About this Mac".

If macOS 10.13 is correct, you need GarageBand 10.5. You could also try to install the older iLIfe version of GarageBand, GarageBand '11, version 6.0.5. On a very old Mac, you may still find GarageBand '11 on the installer DVDs. If you previously owned a GarageBand version from the Appstore, it might still be in your list of Purchases, asKeith pointed out, and then it may allow you to download it from your purchases at the AppStore.

If you never owned a GarageBand version from the AppStore and it is not associated with your AppleID, borrow a newer Mac from a friend or family member, where they can create a user account for you. There sign into the AppStore with your AppleID and purchase GarageBand for free. Then go back to your own Mac, restart the App Store, sign in with the same Apple ID at the AppStore, then check your purchases. Can you now see GarageBand in your Purchases and download it?

Is the system version given below your question "macOS 10.13" correct? You can see the system version when you click the  menu in the upper left corner of the main menu bar and click on "About this Mac".

If macOS 10.13 is correct, you need GarageBand 10.3.5. But the current version at the AppStore is GarageBand 10.4.11.

You could also try to install the older iLIfe version of GarageBand, GarageBand '11, version 6.0.5. On a very old Mac, you may still find GarageBand '11 on the installer DVDs. If you previously owned a GarageBand version from the Appstore, it might still be in your list of Purchases, asKeith pointed out, and then it may allow you to download it from your purchases at the AppStore.

If you never owned a GarageBand version from the AppStore and it is not associated with your AppleID, borrow a newer Mac from a friend or family member, where they can create a user account for you. There sign into the AppStore with your AppleID and purchase GarageBand for free. Then go back to your own Mac, restart the App Store, sign in with the same Apple ID at the AppStore, then check your purchases. Can you now see GarageBand in your Purchases and download it?

If you have downloaded it before, it should be in your purchases. If you have not downloaded it, you can not access older versions.

Did you check your purchases on the App Store?

Not necessarily so. I have had 2 older downloads for older osx's. But they disappeared when updating to Big Sur. I just want 10.4.1!