It depends on what you mean by not using Play Store.
You can install any apk by installing a file explorer app on H8 (e.g. ES File Explorer) and simply navigating the the .apk file and selecting it. Using this method you can install apps not available in Play Store.
If you mean at a lower level then it is no doubt possible to root the H8 and install apks after hacking into the box using SSH. I have no idea how to do this though.!
Many thanks for your quick reply.
I am currently in a country for a few weeks that the Google Play store is banned (blocked) and using a VPN method, for example, to access the Play store, it is complicated... But possible
I understood from your post that firstly the only way to install apks directly, I must install File explorer from the Play store first, and later can install apks directly. If I am wrong, let me know!