There's no Desktop application for Amazon Photos on Linux. Your only option is to upload through the web user interface.
If you have failures, a <div>
pops up in the lower left telling you there are failures, but there's no real way to do
anything with that information. Assuming the errors were not serious (e.g. you ran out of upload space for videos) you
probably just want to retry the failures: especially if you have 25 thousand files.
The only sensible way to extract the list of failures (there were 170 odd in my case) was to inspect the page and copy the HTML node containing the errors.