If I recall, the US S21 Ultra can b e bootloader unlocked via a service on Telegram but only on a specific Android version. After that version, you are out of luck.
I never got to listen to them in person. I heard so many people praising the speakers at the time.
I didn't know there was an M7. If they sounded amazing on the M7, I can't imagine what they sounded like on the M8.
I had an HTC 10 at the time, around its release date as that was the only phone with a Snapdragon 820 available at T-Mobile in my location. It was an ok phone but got better with a custom ROM+kernel. Shame about no dual front facing speakers on the HTC 10 because the single front facing speaker actually sounded great.
@Render
@sh.itjust.works