Sure, windows 10 PC using google chrome browser. Did it over the space of the last few days. Able to save and return to it as necessary.
Had to upload a few scans of passports, my degree (for language knowledge proof), my driving licence and healthcard. Also uploaded the digital photo of myself. These are all jpg images under 1MB in size each.
The physical presence calculator was a PDF that I saved when I did the calculation It's a standard file I guess so it should be similar for everyone.
The receipt for the $630 fee was a PDF too. Again that should be standard for everyone.
There was a section where you could upload other documents to be "considered". I uploaded a PDF letter I wrote with some clarifications to my answers as the silly system doesn't have "United Kingdom" as an option for where you were born or what your citizenship is. I also uploaded a scan of the receipt I got at the photographer for my passport photo as it mentions in the notes that they want to know who took the photo and when.
Do you get to the point at the very end where it asks you to "sign" by typing in your name? When I did it and submitted it the final time it instantly popped up
this page. When I clicked on the "Save a copy" link in the blue box at the top it downloads a PDF file with all my answers in it.