There is a multitude of ways dust can get into there. And I have the feeling that since IBIS, there is a bit more static electricity build-up than before - so the sensors seem to attract more dust. But that just might be my feeling.

Changing lens in a dusty (or even a mostly clean) environment always has a good chance of some transferring into the body. Even if you do it the recommended way with the body mount face down, it means that your lens mount is face up. Dust can transfer from the back element of the lens into your camera. While the closing of the shutter prevents direct dust transfer to the sensor, if any dust is caught between camera and lens, it has a chance of settling on the sensor.

As good way to minimize (not prevent!) this, is to blow out the camera with mount down with a rocket blower in a somewhat clean environment. This stirs up any particles and has a chance to blow them out of the body enclosure.

On some cameras (like the Sony a7 III) sudden accumulation of dust particles on the sensor can also be an early sign for wear on the shutter blades. Here the dust particles are actually tiny shaving of the shutter itself. However, even minor damage on the shutter is usually visible under good light as uneven shutter blade edges. Note, that this is a very uncommon worst case scenario. You might still check yours, just in case.

The good thing is, the sensor is somewhat robust in most modern cameras and has a protective glass or filter pane in front of it. You can order cleaning kits to perform cleaning yourself.

By the way: 2 years is quite a time on a modern camera. I usually have to clean my sensor every other shooting.

I usually do these things in that order of escalation:

1. Remove lens, hold camera mount down, if possible activate sensor vibration, then blow out the mount with a rocket blower. Never use canned air or a compressor. And also do not forget the back of your lenses....
2. If the dust is still in there, I use a "Speck grabber". It looks like a bit of jello on a stick. You dip the stick on the dust and it sticks to the stick. Then you tap the stick onto a transfer sticker and deposit the dust there. If you buy a Speck Grabber, first try it on a clean window, to make sure it does not leave residue. There are cheap ones around that are shitty.
3. Go to the cleanest room and perform a wet cleaning with a cleaning kit. Stick to the manual of the kit. Don't overdo the cleaning fluid. A drop is usually enough. Only use each side ONCE. Buy a kit that fits the sensor size. If you have to go multiple times, you usually leave smear marks.
4. If nothing helps, seek out a service provider who does sensor cleaning.

Useful Tools:

• Illuminated loupe to find the dust
• Speck Grabber to get rid of solitary bigger particles
• Wet Cleaning Kit
• Rocket Blower