If you are just connecting the Wix upload button through the Wix Editor itself without code, then you are better suited going through the Wix Support pages about ut or contacting Wix Support themselves.
https://support.wix.com/en/article/contacting-wix-support
https://support.wix.com/en/article/adding-and-setting-up-an-upload-button
https://support.wix.com/en/article/supported-media-file-types-and-file-sizes
However, as you say that you have actually tried to use code, then what code have you actually used on your site, as the attached picture does not show your actual used code.
The first thing that I would question seeing the title is not defined message, is that when you added your upload button have you connected to your dataset correctly and added a field in your dataset for your users documents that is also a document field type too?
https://support.wix.com/en/article/adding-and-setting-up-an-upload-button#step-2-connecting-your-upload-button
See here for field types within a dataset.
https://support.wix.com/en/article/about-your-database-collection-fields#field-type
Also, there is already a Wix Corvid tutorial with the upload button that you can look at and maybe use.
https://support.wix.com/en/article/wix-code-using-the-upload-button-with-code
Finally, note the process of the upload button itself.
The upload button stores the uploaded file itself and you have to manually get it through the Wix Editor by clicking on the upload button to get the uploaded file.
In the Wix Editor, select the upload button and click Manage Upload Button. In the Upload Button Settings panel, click Go to File, which opens the images that have been received by your site. There you should see the image that the user uploaded.
If you are wanting your users uploads to be saved into an actual dataset, then you need to make sure that you also add a submit button too on your page, which is noted on that how to add upload button support page too.
You need to add a submit button to your page to save user data to your collection.
If you have done all that correctly, then it might just be down to the fact that it is a Apple IOS issue and that os is not defining the correct file type only, even though you have set it up in the button and your dataset etc, wo when they try to upload an image into the document field the error is thrown up.
If that is the case, then there might be nothing that Wix can do about it as it might just be a wait until Apple fix it reply.
