Is my iPhone incompatible with the Bluetooth speaker?

Hello? I am Lee Jung-min living in Deokyang-gu, Goyang-si, Gyeonggi-do, Korea.

There are some problems when I connect the iPhone se 2nd generation and the Bluetooth speaker. Among the Bluetooth speakers, I connect the JBL Flip 4 Bluetooth speaker and I am using a rotor to output the voice-over voice to the built-in speaker, but the problem is that when playing music or in that case, the voice-over output device comes to the built-in speaker and the music is the speaker. I set the rotor to come out as, but when playing music, the voice over voice volume of the built-in speaker suddenly increased. Why? Whenever I do that, my heart is scared. At the same time, I think I'll send the built-in speaker song! While listening to music, even when adjusting the volume with the volume button, the speaker volume decreases and increases, but the voiceover suddenly increases when the volume is adjusted while the music is playing. When music is not playing, the speaker volume decreases and increases when the volume is adjusted, but the built-in speaker voice-over audio output device rotor basic built-in speaker volume does not respond. In other words, the current set volume is maintained as it is before the Bluetooth connection. In addition, when connecting to the BZ-A10 speaker of Britz International, the voice-over audio target was designated as the built-in speaker. It does not switch to and the voiceover voice still comes out as the speaker. For reference, the current software version is 14.2, and I bought this phone in May 2020. IPhone delivery was bought on May 16, 2020 at *** *** *** **** ***. At that time, I didn't know the version of the iPhone se 2nd generation when it was first released, but software upgrades are also ongoing. What are the causes of these two symptoms?

In the next update, it would be great to find out the cause of the symptom and fix it.