you’re correct, that receiver does not have s.port telemetry support, I’m afraid you’ll have to get a new D16 receiver.
Also since you’re splitting mavling to feed the OSD you either have to use a converter that outputs passthrough such as this one https://github.com/zs6buj/MavlinkToPassthru and leave the serial port protocol as 1 (or 2 for mavlink 2) or dedicate a second uart to passthrough telemetry and on that one set serial protocol 10 (in this case you’d also need an inverter like this one Some soldering required)