https://www.interrail.eu/en/plan-your-trip/tips-and-tricks/trains-europe/differences-between-1st-and-2nd-class

https://www.seat61.com/european-train-travel.htm#first-or-second-class

It's not true and I feel cheated "Sometimes the perks of travelling first class even start before boarding the train, with access to lounges and priority check-in". In German they said it is not included. 😥

In a number of other countries, 1st class pass holders have access to the lounges. So it is true.

With a 1st class pass you get free optional seat reservations in Germany, Austria, Czechia, Hungary and some other countries through tickets.oebb.at : add Interrail as a discount and select one-way tickets.

My question is why I did  cant use the lounges when i paid for first class? They trated me like 2class. 

They told me that i haved to pay for the seat from malmö to Hamburg. 

I dont know why. 

In some countries you can use the 1st class lounges and in some you can't. It is up to the railway company responsible for the lounges to decide.

You always have to pay for mandatory reservation even if you have a 1st class pass and the cost for the reservation in 1st class is often more expensive than in 2nd class . During the summer seat reservations are mandatory on the direct trains between Germany and Denmark. 

With obb you get the optional seat reservations in 1st class for free for some countries. 

Because that's DB's policy.

Unfortunately, the ÖBB free 1st class reservations don't work between Hamburg and Copenhagen. But you can book for €3.10 on cd.cz. Reservation on the Öresund trains between Malmö and Copenhagen is not necessary.

Can I use this coupon between Paris and Milano? 

You still need a Reservation for the direct TGV The direct FrecciaRossa is not covered in France

you need to pay for the reservations