I've just been playing around with raw files of the Fuji X-S10, using Hex Fiend on macOS. If you replace the instances of X-S10 with X-T30, then Capture One will open those files.
You could also replace X-S10 with X-T3 but then you have fiddle a bit because that's one character less and the following bytes will move one position forward.
Warning #1: only do this if you know what you're doing. Make a backup of your raw files first before you start editing them!!
Warning #2: I don't know if the result in Capture One is the same as proper support in C1 v21.
Spencer got a reaction from YOUTA in Opening X-S10 files with Capture One v20