Right now, Microsoft Designer is in preview mode and you can only get in by invite. But I put my email on the waitlist and was allowed in after only a few days.
Microsoft is also baking in their AI technology, so that you can start a design with a sentence-prompt. MS Designer lets you start by typing “I want a birthday invitation for my daughter who loves ponies” or “Make me a poster that shares my guest wifi password” and MS Designer will churn out some starting points. And if you don’t care for all that AI stuff, just click Start from a Blank Canvas.