The first thing you should try is checking whether any audio "enhancements" are turned on in your audio settings and turn them off if possible. Your monitor might have such settings included, Windows has a setting to turn its enhancements off, and your PC maker might have bundled enhancement software along with the audio drivers.

Apple's USB-C/3.5mm adapter is the cheapest way to diagnose whether the problem is coming from the headphone end or the DAC end. Make sure to buy from the Apple store to avoid counterfeits, get a USB-C/USB-A adapter if you need one, and make sure to configure it to 24-bit in OS settings. It might sound quiet if you buy an EU model due to regulations, but you should at least be able to tell whether it still sounds off.

If it's the headphone end, the most likely culprits for a headphone problem would be either 1) that your headphone sounds wrong naturally and the previous output was changing the sound in a way that made it sound better or 2) that the earpads went flat and you only just started noticing. If your problem is boomy bass, my guess would be that your outputs have really high output impedance, as flattening pads on closed-backs usually rolls off bass. Beyer treble tends to smooth out and sound less sharp as the pads flatten, though, so I can't make 100% guarantees; if Beyer included another pair of pads, I'd suggest swapping to verify.

For the first, try installing Equalizer APO + Peace GUI (assuming you're on Windows) and using one of Oratory1990's EQ presets. For the second, see which pads Beyer intended for use with the 177X and look for a new pair. Aftermarket pads will change the sound, for better or for worse, so it's best not to skimp. I'd only recommend the first solution in your current case, but the second might be advisable if you have other issues in the future.