Since the latest patch my game has become unplayable. Im going to redownload it. Is there any way I can save my library as I would like to keep copies of lots and households that I have.

Your Library items are located in The Sims 4 > Tray folder
note that it only include your Library items, but not anything else

you might want to also backup:
Saves, Screenshots, Recorded Videos and the Options.ini file, which include your settings
(all of those also located in your The Sims 4 folder).

If you're using mods, keep your Mods folder as well
but in case you've got any broken mods, you would need to check them for updates (where you downloaded them from) before you put them back.

Ive redownloaded my game and it working except it wont allow me to load anything from the gallery or my library. I managed to download a few items but it wont allow e to download anything else. Does anyone know why it would do this.

You may have broken mods and need to clean up your mods folder. Check the list of broken mods in this help section.

Even though your game is running fine with only the library issue, as @Ursine1bear said you may have a mod that (possibly a UI mod like more cas columns etc) needs updating. Only way to test is take mods folder out, see if game library works. If yes then you will need to check you have the most updated version of all mods in your mod folder before putting them back into your game.