Solved
2020 Sims 4 CC won't allow me to save to my library but will work in game
Product: The Sims 4 Platform: PC Which language are you playing the game in? English How often does the bug occur? Every time What is your current game version number? 1.61.15.1020 Wh...
@nlizabeth If you save a Sim with any custom content they will not appear in your Library unless you check the box labeled "Include Custom Content" in the "View Content By" menu. Please verify that you have this box checked and let us know if this fixes your problem.
Good luck, I hope this helps :D
