Latency doesn't work with PulseAudio on linux

I guess the latency offset in your screenshot is just Pulsaudio calculating time to buffer sizes with given sample frequencies and trying to arrange this parameters with ALSA. Changing the latency offset there not showing an effect might just be an ALSA driver not supporting much variety in buffer sizes.

To get an extra buffer you could add a null sink to use module-loobpack's latency_msec like so:

pactl load-module module-null-sink sink_name=delayed
pactl load-module module-loopback latency_msec=2000 source=delayed.monitor sink=alsa_output.pci-0000_00_1b.0.analog-stereo

Then you have to combine the null sink with your bluetooth audio.

I've had the expected huge delay when testing this simple setup without module-combine-sink like this:

paplay someaudio.ext --device delayed