Ear buds or IEMs typically have a much higher sensitivity than full sized headphones. The higher the output power of your PC's headphone out, the louder your earbuds will be at any given volume %.

There isn't anyway around this except to manually change the volume whenever you use your earbuds.

It sounds obvious, but have you checked your sound settings?

It's possible that the default volume slider is tied to the output for the headphone jack. But earbuds are wireless and may have their own. If that sounds level on the PC is maxed at 100%, it would cause what you're talking about about

You generally want your source to cap at 80% volume, but if that's still to loud go lower obviously. But you don't want it so low you're earbuds are turned up to 100% either.

Volume control on buds or headphones should just be for fine tuning. And you want it to be around the middle for normal use.

This has been an issue for ages on the volume's slider control. I am guessing it is coded to operate linearly, and our perception of sound volume is non-linear.

It's extremely aggravating. The usable range for the control is indeed in that lower 20% or so, and it's a small slider so it's hard to adjust it within that narrow range so that it's just right.

I’m going to assume you’re using wired headphones and earbuds:

Every device will have a different sensitivity - IEMs, headphones, powered speakers, passive speakers, etc. and it varies wildly between different IEMs, different headphones, and so on.

That means every device requires a different amount of power to drive it. Your PC doesn’t know what device you’re using - it just outputs the same amount of power at the same volume level, and it’s up to you to adjust it to the appropriate level when you’re using a different device.

Now, different output jacks on the PC may output different relative levels even at the same volume setting. The headphone output will have a bit of extra power driving it, raising the level to drive passive wired headphones and earbuds, while the stereo output will have less power because it’s assuming that your speakers have their own separate power source - either built into powered speakers, or with a powered amplifier in the line between the PC and passive speakers.

Assuming you’re using the same jack for the earbuds and headphones, the volume difference is because your earbuds are more sensitive than your headphones. The earbuds require less power to drive, and the headphones require more power to drive. Windows simply spits out the same amount of power to the headphone jack at its volume setting, so the earbuds are louder and the headphones are quieter, even though they’re receiving the exact same amount of power.

If you don’t like adjusting windows volume, one solution is to get a USB headphone amp. Great headphone amps can be had for around $100 from brands like Topping, JDS Labs, Schiit, and more. It’s a competitive market so there are tons of options. This won’t even out the levels between devices, but it will put a nice volume knob at your fingertips, along with the jack itself for switching devices. Many of them also reroute audio to your speakers at the touch of a button. You’d then simply “mix” the volume level on your speakers to match your preferred knob position. Another bonus is that there’s no analog audio signal swimming around with the other noise in your PC, as it’s now leaving digitally over USB, so the audio quality is usually noticeably cleaner.

There are some old school and professional headphones that require headphone amps to drive, because even at 100% windows volume, most PCs will simply not output enough power. Whenever you’re shopping for passive headphones, you might see reviewers say things like “these headphones are easy to drive” or “hard to drive” - they’re referring to how much power is required to achieve acceptable listening levels, and advising whether you’ll need a beefy amp or not. Most consumer headphones these days are designed to be driven by weaker power sources like those found in phones and PCs. But again, it varies wildly - and what you’re experiencing is a small variation in power requirement between two devices.

I've always had issues with volume levels on Windows, so I stick with Equalizer APO for my solution now. Just set a preamp on the device in question and set it to a negative number that sounds and feels right, plus there's a handy on/off for every setting you choose. Other people might have better options, but I'm lazy AF, and it works for me.

Biggest thing I love that program for is setting a lowpass filter for my Bose, so that knocks in videos don't sound like someone is knocking at my door, then just switch it back off when listening to or working with music. Great tool.

Edit: you can have individual settings per device this way as well.

Same, on windows I have had changed the front levels of the speakers to work in the range 0-25%. But I never know how the hell to reach that dialog in an easy way. I couldn't explain how I did it.

This link explains something else but the screen captures are similar. But for "front" you have to scroll down. https://www.abyssmedia.com/isound7/how-to-hear-line-in.shtml