I'm trying to upload files (images, videos, archives) and I can't. What is the problem?

Try to upload a JPG or PNG and make it smaller, usually this is the problem. If you're uploading an image, there's no need to upload images larger than 1000px in width. Make sure your files are not "300DPI" in resolution, you don't need that on your website, it's for print only.

If you're trying to upload files directly from your camera, try to resize them before uploading, if you're uploading a photo from your iPhone, it may be in HEIF/HEIC format, which isn't supported - try to convert it to JPG first.

Is there any file size limit?

There should be no limits in the website builder app, but you may have some limits set by your webhosting company. Sometimes it's possible to login to the "Control Panel" and set higher limits manually but in most cases you may have to ask your webhosting company for assistance.