Yellow dot

Again, if you downloaded TikTok via Test Flight, it is a beta version. Whether or not, TikTok can "hear" is unknown. If you are concerned, then remove the app ... and don't use Test Flight either.

Regardless, there is no "yellow" status indicator in iOS. There is an "orange" one, and that would indicate that your phone's microphone is enabled.

Ref: Status icons and symbols on your iPhone - Apple Support

Test Flight is used to try out beta software. If the version of TikTok you downloaded via Test Flight is a beta, then you need to contact the TikTok developers as to why a "yellow dot" appears next to their app.