Hi @Rebecca Maxson
Welcome to Q&A forum ~
Could you please check the version number and update channel of your Microsoft 365 Apps via clicking File > Account > Product Information > About PowerPoint？
I suggest you go to Troubleshooting part of the article "Create professional slide layouts with Designer", and then select " I don't see the Designer button".
According to the article, please make sure your subscription is not Office 365 Germany Germany.
Besides, you have turned on Office connected experiences.
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