I have no idea why the HA manufacturers don’t support aptX LL other than there appears to be an up-front cost and a per device cost to use aptX. Might there be an additional power drain for decoding aptX LL?
As for using the ConnectClip as the streamer for TV, there would be the latency in the Classic Bluetooth implementations along with the latency in the MFI connection to the aids. Oticon doesn’t seem to specify the latency due to the ConnectClip in documents I have found. They do specify the latency of the combination of the TV Adapter 3 and hearing aid as 25 msec for analog audio input and 28 msec for digital optical (TOSLINK) and 45 msec for Dolby Digital (digital optical). The latency for aptX LL is approximately 40 msec according to web page I found at apex.com so similar to the TV Adapter.
One way to get rid of the latency issue is to use wired headphones . I have some old Beyerdynamic DT 770 Pro headphones with very large ear cups that seal well - nice passive noise reduction. My OPN S 1 aids don’t feedback with them so that is good except for the wire
I have found that even with the fairly low 28 msec latency of the TV adapter (my ancient TV doesn’t do Dolby), the sound is better for me if I mute the HA microphones, or better, mute the TV/sound bar audio AND the HA mics and listen only to the streamed audio when listening to accented or soft voices. It seems that my ears/brain prefer a single input rather than two, one of which is delayed a bit. I have seen documents where the manufacturers of aids attempt to control the latency to minimize so-called spectral or timbre effect - one paper seemed to indicate that some HA users with open fittings could detect latencies longer that 10 msec. I don’t have a true open fitting as my aids are set to use a so-called bass dome with two tiny vents.