433 MHz Transceiver - understanding OOK demodulator parameter 'OokFixedThreshold'
The Y axis on the graph illustrating demodulator threshold settings is labeled &quot;RSSI [dBm]&quot; which suggests the dB value in RegOokFix is relative to some RSSI value, the question is what value?
RSSI values go from 0 dBm (RssiValue = 0x00) to -127.5 dBm (RssiValue = 0xFF). The procedure recommended to optimize OokFixedThresh (shown in the flow chart in Figure 12.) is to monitor data output starting with the default OokFixedThresh setting of 6 dB and incrementing it until there is no glitching. This implies incrementing RegOokFix increases the threshold level above the minimum RSSI level of -127.5 dBm, eg. -127.5dBm + 6 dBm = -121.5 dBm.
However you say,

I've followed the procedure, everything works fine, no issues with the
receiver. The value I use is 0x60 / 96 dB.

-127.5 dBM + 96 dB = -31.5 dBm. If I have interpreted the datasheet correctly then your receiver should have very low sensitivity in 'peak threshold' mode.