What are the best apps for posting my traveling photos "on the fly"?

It doesn't meet all your requirements, but consider the Google Photos app on mobile. If you enable the assistant, the AI can create albums and videos for you from the photos you've taken on a trip. You can also create albums and share them with the world or particular people.

If you have an iPhone you can create an album that you can share with other iOS users, and anyone can add pictures to the album. You can also expose a public link to the album that anyone can view in a web browser.

Exposure is more of a blog platform, but it's very much used for travel photos. The UI is really great. Are using it for my own blog as well.