Some further information for those building this:
For info, my F3 flight controller code is Betaflight 3.1.0, and the ESC code F_H_40 V16.5. There is later Betaflight code, but didn’t want to risk trashing the FC by reflashing it.
Channel reception (Frsky)
Initially, I got it to bind fine, produce telemetry (RSSI, Voltage by connecting VBAT to A1) back to Taranis Q X7 etc - but no channels appeared in the Betaflight receiver page. Looked at the RCIN line with a scope and could see the packets fine, and they changed as I moved the sticks, so it looked good. Messed around a lot, no obvious missing links on FC. No good. Tried rebinding. No good. Tried rebinding again - and it all worked. No idea why. So, if that happens, rebinding may help.
On the Betaflight configuration page, tried to set motor protocol to DSHOTxxx, and - no DSHOT protocols listed. Couldn’t find out why - it defaulted to ONESHOT125. Lot of fiddling around. No good. Then to find out if the FC code version did support DSHOT, in CLI, entered
That listed DSHOT150/300/600 as available motor protocols, so set a DSHOT protocol with
set motor_pwm_protocol = DSHOT300
and that worked. DSHOT still not listed in the protocol list on the Betaflight configuration page though, so it just shows nothing - therefore that list allows one to move away from DSHOT, but not to it. No idea why - the same configurator lists DSHOT OK for an Omnibus F4 FC.
Anyway, hopefully this info is of help to someone.