u still did not say HOW u installed the apk.

typically, to sideload an app, u first install ES file Explorer (esf) from the TV playstore.
it is a very useful file manager - to install, move, copy, delete, etc.

if u use esf, u will see a message at the end - whether it is successfully installed or not.
if it is successful, accepted, u see the message, continue.
if it is not, u will also see a message - meaning the TV has rejected this app.
the tv runs on google androidtv, hv certain controls to protect it from harmful malware embedded in certain 3rd party apps.
i have come across a few apps where the tv will simply reject it.
these are usually "dubious" third party apps.
the majority of apps will be fine.

as for where to find these sideloaded apps after installation...

settings (bottom of tv UI), apps, downloaded apps - all successfully installed apps will be there.

Cannot.

Becos the app is not a google androidtv approved app.

Try to install a different launcher.