Shameless plug but I use Lemmy Keyboard Navigation (RES-like extension for keyboard navigation)

Lemmy-UI and Mlmym with tampermonkey script lemmy-keyboard-navigation

Fax

BBC

Apollo on mobile

RES+old on web

Bladder Runner just REALLY wants to go to the toilet

Bood*

Dune

For your 2nd point, I made a script. It works with arrows so you may or may not like it. Also I see a PR was opened yesterday on Lemmy-ui for J-K navigation

Now that I made this keyboard arrow navigation script answer is … YES!

https://github.com/vmavromatis/Lemmy-keyboard-navigation