"It can be done but is relatively difficult with such a camera."

I found out the hard way that as cameras and lenses changed and got better, the only way to change the body or change the lens on an "all-in-one" is to sell the camera and buy a new one. Also, the sensor on the Sony RX-10iv is even smaller and more depth of field than a 4/3rds sensor. This also affects ISO and diffusion. Luckily, software is very good these days for both issues. But there is a strong chance imaging will require post processing especially with the astrophotography. And even as good as the Sony RX-10iv is for telephoto, individual lenses for a system will tend to be better both in focusing and imaging quality.

"I would look at adding proper lenses to the system you have."

User ID is correct. How much do you want to do and how much better do you want to do it. You may be able to buy, and even further upgrade, bodies and lenses and have more than you will with the Sony RX-10iv. Do not get me wrong. The Sony RX-10iv is a good camera with pros - and cons.

"If you do not have a proper system yet, I would look at a used Olympus/OM or Panasonic body coupled with a Olympus/OM, Panasonic, or one of the third party 4/3rds wide angle and telephoto lenses (5mm to 10mm at the widest end for astrophotography and 150mm to 600mm for telephoto)."

4/3rds has a bigger sensor with what could be less downsides than the Sony RX-10iv. Again, if you don't have a good system camera yet, I suggested a system that could meet your needs very well and still be cheaper (lighter and smaller) that full frame or APS-C. But if you already have a system, really consider UserID's suggestion.

DSLRs a superb system of systems with which to photograph images. I know for certain that DSLRs take photographs every bit as good as any mirrorless camera. I don’t give a hoot what others say! If you know what you are doing, the DSLRs will deliver the shots, and they will do so for less! No rolling shutter, better low-light visibility through the viewfinder. While mirrorless cameras may give you ”what you see is what you get,” in the view finder or the LCD, as I said before, if you know what you are doing, mirrorless isn’t any better!

There is such a thing as “good enough!” DSLRs are more than “good enough!” Don’t fall for the hype!