I am using GarageBand 10.4.6. Under the loop section I am only able to access some of the green loops and none of the blue loops. The display on the top right shows I have hundreds of loops, but few can be accessed.

Have you already downloaded all items of the Sound Library? Check the Menu item GarageBand > Sound Library and use the command "Download all available Sounds". Loops that need downloading will appear as grey and disabled.

You could also try to rebuild the Loop Index.

• In the Loop Browder click the pop up menu at the top of the Loop Browser, where you switch between the available loop packs. At the bottom of the menu is the item to reindex all loops.
• After rebuilding the loop index some grayed to items may be showing a download arrow. Click this arrow to download the loops, that are not yet available and keep this option turned off.
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Also, there is a checkmark in the GarageBand Preferences > Loop "Filter for more relevant content". This will disable loops, that are in a different key or tempo. I prefer to have all loops available.

It used to be that it depended on the musical key you had set. I believe there is a setting to ignore the key.