Hello @Stefan,
Thank You for posting your query onto the Forum.
Have you tried using the simple % format. Because if you try using the Format function the numbers will get converted into the text. And will simply either show the figures in the decimal figures or will show blank as is your case.
By the way are you trying to analyze the charts using slicer where you select Numbers and the Percentages option and accordingly the charts changes.
I’m also providing a link below where similar type of query was asked onto the forum by one of our member and how the solution was achieved.
Hoping you find this useful and meets your requirements.
If you need anything just give a shout.
Please Note: Click on the link to view the entire post and not on the expand/collapse button.
Thanks and Warm Regards,
Harsh
Providing one more link.