I would connect it to the receiver if possible. Some TVs do not passthrough all audio formats, which can cause unnecessary transcoding.
My setup: FireStick ← HDMI → Denon AVR-X4300H ← HDMI → LG B7 OLED
The FireStick sends AAC audio to the Denon as PCM, up to 5.1 channels.
I have connected the FireStick to an HDMI input on the LG TV, but that was several months ago. It worked fine. There was no lag navigating menus, etc. I played a couple of movies without issue, but I did not do any extensive testing.
One more thing to note is that the FireStick (4K or 4K Max) does not output 7.1 audio. At least with Plex, it is a maximum of 5.1 channels. Not an issue for me as my speakers are 5.1, but thought I’d mention it.
Here’s a post with info on how the 4K & 4K Max handle various audio formats. Someone asked about 7.1 audio support, so I ran some quick tests.
