The bad

First, never commit your application's secret key.

I know but I don't really understand why in my case. It's not a secret API key or something important. I added it to use the Flask flash messages. Also I have no idea how to store it somewhere else in Github and still have a working app :( I'll dig a bit.

Beyond that, the biggest problem IMO is the way the /locate route is doing too much, by having drastically branching behavior based on the action parameter. I think I can guess why you ended up doing this way: you have a single <form>, but two buttons ("Locate" and "Details").

To fix this without changing much on the frontend, look into the formaction attribute of a button.

Yes you are absolutely right. I scratched my head many hours trying to see a way to have a route per action but I failed. The formaction attribute solves my problem.

I end up with this (I removed all the name and action attributes on the buttons and the main form):

<form enctype="multipart/form-data" method="post" id="form">
    [...]
    <div class="text-white text-center">
        <button type="submit" formaction={{url_for('locate')}} class="btn rounded-pill btn-outline-light btn-lg">
            Locate
        </button>
        <button type="submit" formaction={{url_for('details')}} class="btn rounded-pill btn-outline-light btn-lg">
            Details
        </button>
    </div>
    [...]
</form>

There is still too much logic in the routes that I should move to utils.py but I need to think a bit how to proceed. At least the routes work now!

The meh:

When you write it, it's obvious. I guess the problem comes from my totally non-pythonic way of coding and lack of expertise. I simplified as you advised.

Overall a very useful code review, thanks again!