Last time I tried, it was not at all well documented how to upgrade to Catalina when your iMac's boot drive is 1) an external SSD and 2) not (yet) formatted to

Last time I tried, it was not at all well documented how to upgrade to Catalina when your iMac's boot drive is 1) an external SSD and 2) not (yet) formatted to APFS. Giving it another try now, but unless it suddenly got a whole lot easier I'll probably be passing again. Have it on my 2016 and 2019 Airs though, no issues.