Open Google Play on your Chromecast, Xiaomi, Shield or any Android TV box. Install TiviMate, IPTV Smarters or OTT Navigator. Allow the app to access files so it can read playlists.
If your provider offers an Xtream Codes portal, use the username/password option — it saves you from uploading an M3U file manually. For manual import, put the file on Google Drive or USB, then choose "Import Playlist" → "Local file" inside the app.
Go to Settings → Playback and enable Hardware Decoder (MediaCodec) for 4K channels. To customize the remote buttons, TiviMate has a Remote Control section where you can assign a long press to the menu, favorites list, etc.