Cannot select my Akai MPK Mini 3 midi controller in Audition v24

Video 1: there was no music recorded. The keyboard shows up in the inputs section just because it's a USB connection, and that's a bit misleading, quite frankly. The maker of that video was in for a rude awakening if she tried to record MIDI data in Audition 2019, because it can't. MIDI recording has only ever been possible in one version of Audition - and that was version 3 where it was added as a beta feature. Since then Adobe policy has been that no beta features were to be allowed in released software (a situation rather forced upon them by the Sarbanes-Oxley legislation regarding software 'completeness') so all MIDI keyboard recording was dropped.

Video 2: There may have been an audio recording because he likes the internal sounds, but he wasn't using Audition anyway, so that video's moot.

Video 3: He's using Reaper!

MIDI as far as recording music is concerned only consists of data in the form of turn-on and turn-off note values with some additional values about velocity, etc. It's a very old serial protocol that is now rather outdated - it's  very slow by modern standards (32k). Most DAWs can record it, but Audition can't any more (see above). A lot of people are mightily pissed off about this - mainly because they assumed that it would when they bought it, and then get the Nasty Surprise: Audition isn't Music Creation software. It's an audio editor that now has very strong links with Premiere, and that partly explains the situation; Adobe bought Syntrillium specifically for the audio expertise of its development team, and as Adobe has always been a picture-based company, music creation didn't really come into it. So to state it baldly - Audition will record audio data only - it won't record MIDI data. There has been a convoluted attempt to make it 'cheat' but quite frankly it's not worth considering.

Several suggestions have been made - the best one being Rewire - which would let Audition synchronise with a basic external MIDI recorder, and this was also tried with Audition 3. Unfortunately it wasn't that well implemented and that led to a lot of frustration so it got dropped too. Other suggestions included working with timecode in other ways, but that was massively complicated to get working. I tried it once and gave up.

The most workable solution has, in fact, been to use Reaper for MIDI input - mainly because it was cheap, I think, but also because its developer was very responsive to suggestions for improvements. And he didn't have to answer to anybody so it all happened quite quickly - people liked that.

Where Audition scores in music production is as either a mixing tool, or for mastering. A lot of ProTools users use it for mastering because PT is actually pretty useless for it, as far as I can make out. Obviously, the PT users won't admit that - well not in public, anyway...