Ah, yep. That makes more sense. I'll dig out an old intervalometer and try that.
I realise I'm operating a bit out in the wilds with how I use the camera. It's just frustrating that this technique did work perfectly with my cheaper and more basic X-E3, but is being blocked by what's basically a programming fault in my theoretically better X-T4. At the end of this, I won't be surprised if I'm left still unable to do it on the T4. Just want to try everything I can to make sure it's not a user issue before submitting as a fault and hoping it gets patched in an update. I would try reverting to my old camera for timelapses but a waterproof housing failure left it with... issues 😆