Most likely your PC is putting out a lot more power by default, which it can afford to do because it's plugged into an external power source all the time. If the output is too low for your monitors/speakers, you can use an Amplifier like this to boost volume output. If you want to get adventurous, I think the impedance on the LyraT is 8 Ohms, knocking that down to 0 Ohms by modifying the PCB (which is probably what your PC is doing) will give a corresponding increase in volume. Lower impedance generally results in lowered sound quality however.

Best way to get volume up if you don't want to get new speakers/monitors is using a small amp.

Edit: From ESP32-LyraT V4.3 Hardware Reference

To switch between using headphones and speakers, the board provides a digital input signal to detect when a headphone jack is inserted and a digital output signal to enable or disable the amplifier ICs. In other words selection between speakers and headphones is under software control instead of using mechanical contacts that would disconnect speakers once a headphone jack is inserted.

So it looks like the board has the ability to enable or disable to onboard amp depending on how it's plugged in.