The 3.5 mm headphone jack on the MacBook Pro (14-inch, 2021) or MacBook Pro (16-inch, 2021) features DC load detection and adaptive voltage output. Mac can detect the impedance of the connected device and will adapt its output for low- and high-impedance headphones, as well as for line-level audio devices.
When connected headphones with an impedance of less than 150 ohms, the headphone jack provides up to 1.25 volts RMS. For headphones with an impedance of 150 to 1k ohms, the headphone jack delivers 3 volts RMS. This may remove the need for an external headphone amplifier.
The built-in digital-to-analog converter supports sample rates of up to 96 kHz.
Reference : Apple Support - Use high-impedance headphones with new MacBook Pro models
After seeing the reviews & tests that have come out, it seems like the quality has not improved much from the older generations just the fact that it can now drive higher impedance headphones and give better volume output. This is unfortunate and thus won't eliminate the need for a good external DAC(Digital to Analog converter) & AMP(Amplifier) for a good Hi-Fi(High fidelity) audio system.