Hi Jan,
Thanks for posting in the community. We are happy to help you.
I can reproduce the same situation when opening XLS file in Excel for iOS. Unfortunately, this is a known limitation. Unlike Excel desktop applications, Excel for iOS does not currently support editing old file formats such as XLS files. In this case, you need to edit the XLS files in Excel desktop app (Excel for Windows or Excel for Mac), Or if you're willing to let Excel for iOS create a copy and convert the copy XLS file to the supported file format XLSX, you can edit the file in Excel for iOS as well (click More in the error message and choose “Save a copy” to the same location, at which point the format of the copy file is XLSX).
I understand the inconvenience you are experiencing. In this case, I sincerely recommend you send feedback to the Excel Product team as they constantly check customer reviews and feedback. And a lot of the features are developed and improved based on customer feedback.
I suggest you report the issue and provide your feedback by the following methods, which are the proper channels for getting attention from Microsoft Excel developers.
1. Post your feedback in the Microsoft Excel Community where other members also post feedback and vote. The higher votes, the more attention the related team will pay on.
2. Use the in-app feedback tool to send your feedback: go to the Home tab > Click Help & Feedback button in the left sidebar (Gray circle with question mark)> Tell Us What Can Be Better
Appreciate your patience and understanding, and Hopefully Microsoft will make improvement soon.
Hope you having a nice day.
Sincerely,
George| Microsoft Community Moderator
