First of all, I'd like to thank everyone that has contributed to the discussion! Were it not for your recommendations/suggestions/endorsements, then I might not have found a valid alternative.

Secondly, I've taken every single recommendation pretty seriously. As such, I've either installed them to see for myself if I was able to reproduce the functionality found in the gif found above. Or, didn't install them to begin with due to the suggested installation methods not passing through my (rather) strict policy on software. Regardless, in the end, I've only found two pieces of software that satisfied the bill: Kate and KDevelop.

KDevelop is pretty cool, but is more of an IDE rather than a text editor. As such, I've landed on Kate.

But, perhaps more than anything, I've come to really appreciate Emacs (and Neovim). And, perhaps more than ever, I feel ready to take them on 💪. Wish me luck 😊.