I'm not totally certain about this, but judging by how the files in the Island Rum download haven't been updated since March of 2018, I'd guess that IR itself is static. IR uses a manifest, much like Tequila, to update CoH, and that's something we control, not Manga. It does not to my knowledge, which is admittedly limited, get updated every time the game needs updating, and the Mac experts I talked to agree with me in this judgment. This isn't going to help you out very much, Ringu, since you're going to be stuck with 10.15, but people who don't want to update to 10.15 should be able to continue playing as they have thus far.