This is interesting. I just tested the following codecs and formats from a Sony A7SIII, which is identical to the FX3 from a codec and format standpoint. FCP 10.6.5 and Ventura 13.3.1(a), Pro Video Formats 2.2.4, Quicktime Player 10.5 (1154.4.2). These were all at 23.98 fps (indicated as 24 fps on the camera menus).
I tested them on an M1 Ultra Mac Studio, M1 Max MacBook Pro 16, and 2017 iMac 27, ALL running the above versions.
All clips worked on all machines in FCP.
On the Intel iMac 27, Quicktime Player would not play the XAVC-S 10-bit 4:2:2 and XAVC-SI 10-bit 4:2:2 clips. Also on that machine, the icon images would not display in Finder. This is despite the clips working OK on that machine in FCP.
Summary:
4k/23.98 XAVC-S 10-bit 4:2:2 - would not play in Quicktime Player on 2017 iMac 27, Finder icons have no images.
4k/23.98 XAVC-S 8-bit 4:2:0 - FCP, Quicktime and Finder icons worked on all three test machines.
4k/23.98 XAVC-SI 10-bit 4:2:2 - would not play in Quicktime Player on 2017 iMac 27, Finder icons have no image.
4k/23.98 XAVC-HS 10-bit 4:2:2 - FCP, Quicktime and Finder icons worked on all three test machines.
4k/23.98 XAVC-HS 10-bit 4:2:0 - FCP, Quicktime and Finder icons worked on all three test machines.
Notes:
XAVC-S uses H264, XAVC-SI is All-Intra, XAVC-HS uses HEVC.
I don't know why the material behaves differently on the 2017 iMac 27.
Re any MP4 material from the FX3 or A7SIII, FCP cannot read timecode from that variant of the MP4 container format. This can be worked around with some 3rd party utilities. That is likely due to lack of industry standardization on timecode metadata representation within the MP4 container.