After moving to Mojave I lost the Euphonix/Avid Artist Controllers, possibly a driver issue, haven't found a solution for that as yet. I had to reinstall waves, some of the Abbey Road Mastering Plugins went AWOL, but a reinstall solved that. I am getting warnings about the imminent loss of non 64 bit software but some (admittedly now ancient) stuff I still use, such as adobe CS6 is still hanging in there. Presumably OS10.15 will no longer accept any 32 bit software, at least Apple are giving notice in advance.
I should also mention, standard practice for me is not to simply upgrade my system SSD, rather, clone it, remove it, pop in the clone and upgrade that. I am assuming that a Carbon Copy Cloner cloned drive should work as well as directly upgrading. The reason I go this way is simple: Never break a working system. Sadly, this method is rather difficult with current Macs, where swapping out the mass storage is either cumbersome, or indeed impossible. Still using a 5.1 Mac Pro here, upgraded with SSDs and a metal compatible GPU.
I've set up everything from scratch on a 2018 Mini. Logic works very well, but with the change to Mojave, I've lost some plugins that worked fine on Sierra. The only one of significance is Melodyne Editor V2 which would have to be updated.