Hello Alvinpoppy,
Just to clarify, does the issue only happen when trying to send the files to the WhatsApp application, or does it happen with other files and applications as well? That information will help us plan how to proceed.
To ensure the correct process is being used to send files from the Files app on iPhone, please check out this link, which may help: Send files from Files on iPhone
Send files from Files on iPhone
You can send a copy of any file in the Files app
to others. If you have a document you want to send that isn’t digitized, you can scan it with Files first.
Send a file
1. Touch and hold the file, then tap Share.
Tip: To send a smaller version of the file, tap Compress before you tap Share. Then touch and hold the compressed version of the file (identified as a zip file), and tap Share.
2. Choose an option for sending (for example, AirDrop, Messages, or Mail), then tap Send.
Please also check out this link, which has information on using the Files app, and saving content, which may be helpful as well: Use the Files app on your iPhone, iPad, or iPod touch
Thanks!