Early versions of the official standalone Tor Browser (versions 8.5 through early 9.0 builds) occasionally bundled backward compatibility for older Android versions.
Go to Settings > Security > Check the box next to Unknown Sources to allow non-Play Store installations.
This is normal for the Tor network. The connection is slower by design to protect your anonymity. Connecting to Tor bridges can sometimes help in restrictive networks.
: The Tor Project ceased updates for KitKat years ago to focus on secure development for modern platforms.