Media Encoder version for PPro CC2017

You're stuck forever, in this case, until you either update your version of OSX or get an entire new Mac. You can no longer download any version of the Creative Cloud apps earlier than 2019, which required Sierra or newer just to even install at all. The last version that was compatible with El Capitan, Media Encoder CC 2018, became permanently unavailable as of November of last year to comply with Adobe's availability policy which went into effect in May of last year. That policy restricts availability to the two most recent major versions - specifically, most releases of the current year's version plus the most recent minor build of the most recent point release of last year's version.