Dear Danny,
Good day! Thank you for posting your query in our community.
Based on your description, when you clicked the Browse button in the Insert Pictures window, there was no response. I tested it on my side, and the result was the same as yours.
On the one hand, we’d suggest you provide feedback to the related team by clicking File > Feedback within Excel application. This feedback will directly go to them so that our related team can pay more attention to this issue.
On the other hand, you can try the below workaround to insert the picture into the header. Please check if the following steps help or not.
- Please make sure the picture is a local file.
- Click Picture under the Header & Footer tab. The Insert Pictures window will appear.
- Type any word in Bing Image Search, and press enter. The window will display !!ERROR!! as shown in the below screenshot.
- Please click "Work offline", then File Explorer should pop on, and you should be able to insert the picture. After that, you can select one cell, and the picture will appear in the header.
Appreciate your understanding.
Sincerely,
Jazlyn | Microsoft Community Moderator