Are you looking to make a specific journey or just looking for general information?

OBB Nightjet are the main operator of dedicated night trains with sleeper/couchette and seated accommodation.

https://www.nightjet.com/en/

This brochure lists all their services and other associated Euronight routes.

https://www.nightjet.com/dam/jcr:f7e9ecef-9494-4cb9-b265-51c305ab103e/nightjet-folder-2022.pdf

There are other services across the continent, both sleeper/couchette type and regular trains running through the night.

Italy, Sweden, Norway, Finland, UK for example run their own sleeper routes. France still has a few couchette services south from Paris, Germany-Denmark and Sweden has 2 operators.

Because there are no direct night trains between those destinations. At least not between Amsterdam and Paris, and I think the Paris Milano (or was it Torino? ) didn't come back after covid.

Most international night trains are now run by Öbb nightjet, you should check their website for direct connections. 

It's okay to do, if you have a proper bed (Couchette or Sleeper). But I prefer day trains. It's more comfortable, you get to see the landscape, quicker too...

When you do it, be prepared for some delay so don't plan potential connections too tight. Have a buffer of some hours. But it's a nice way too travel, saving a hotel night and time between point a and b (if a direct night train runs between them). 

There are many night trains in Europe but not on the routes you are suggesting. ÖBB operate many of the night trains under the brand Nightjet. If you Google nightjet routes you’ll find lots of information. The other brand is Euronight. Some other operators have internal services such as in the UK and Italy down to Scicily. There are a couple of trains in France as well

I agree with Brendan and I prefer day trains. However have used ones from Wien to Bucuresti and Sofia to Istanbul this year. As he says be prepared for late running as night trains have a very low priority needing to slot in with heavy freight services. A bit like in USA.