when adding : http://dr3amingth1ngs.tumblr.com/rss Akgregator says "feed not found from http://dr3amingth1ngs.tumblr.com/rss" FireFox is happy to display it as such, and even offer "subscribe with Kontact" v5.7.3 which isn't in your drop down.
The URL is redirected to https://www.tumblr.com/privacy/consent?redirect=http%3A%2F%2Fdr3amingth1ngs.tumblr.com%2Frss. Not really surprising it doesn't work.
Sigh. Go past that. Attaching RSS.
Created attachment 113035 [details] RSS as returned and saved from FireFox
I can't reproduce with the file you attached. the articles are loaded without issue
What version of Aktegator do you use?
master
Can confirm this issue with Akregator 5.7.3 on Debian. Forgive me if this had already been brought up, but from what I've read elsewhere this appears to be a GDPR-related problem, Tumblr is trying to issue some sort of consent form and Akregator doesn't know what to do with it so the RSS comes out as invalid. The catch to this is that Tumblr only does this if it detects you're making the request from inside the European Union (I'm in the United Kingdom) if you're not, it just serves a normal feed. So if you want to test for this outside the EU you'll need to use a proxy that's inside the EU.
Thanks for confirming it's not an akregator issue. The feed is invalid because tumblr redirects to another page.
Ideally we would sync cookies between browser and KIO so that once you gave your consent on the browser the website knows when Akregator does it, but this is a story for another time