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Well - I had 'Latest release' 1.12.2' & 'Latest Snapshot 1.13-pre5' showing in the launchers dropdown box so I'd guessed it's was there (launched it today & the snapshot profile changed from 'pre2' - I usually use multiMC as my launcher)
I went ahead & created a new profile (snapshot2) with 'pre5' - as you suggested - & now Amidst show the title of 'snapshot2' but it's in red & has 'not found'. So I'm guessing that Amidst doesn't recognise the 'Latest snaphot' profile of launcher & you have to create a new one for Amidst to recognise it
Changing 'snapshot2' profile to 'pre1' all the way up to 'pre4' & it shows up OK until you click on the arrow - it then shows 'failed loading' & up pops an error screen (& yes - I did launch the profile in launcher to download all the necessary files first before I started up AMIDST)