Hi Chas,
I am just fallen into the rabbit hole of investigating how to upgrade my X-T4's video sound...
Loving the idea of time code sync, I am now quite concerned that the X-T4 doesn't support it, although I have already seen different statements on the net, like here:
https://youtu.be/xja27RmvbhE?si=hIch3Tu_MH_pWSBH&t=571
I have to admit, this guy's "explanation" gets quite confusing in his further discourse ...:)
BUT, as you wrote that you use Tentacle Sync for Windows!, did you also try with their windows-only software "Time Code Tool" which you find here?:
https://tentaclesync.com/timecode-tool
Would love to here if you found a workaround with the XT4
Best,
Simon