For which trains are you asking exactly? Otherwise it´s hard to give e answer

Eurailwebsite and Eurailapp use data from the EuropeanTimetableCentre and get less updates :) 
(Not all companies load their timetable to the Centre ) I trust always the local railplanner times more as they get more updates :)

The Railsystem is at the beginning a bit difficult but once you enyoed the experience you get used to it :) 

Nighttrains can be a good option the question is which comforts are offered and how much it cost :) 
Some can be reserved just 60days in advance others even 6months in advance For which Nighttrain rules you keep an eye on? Maybe i can provide links of the trains (with pictures) so that you can see what you book :) 

French Rail offers only Couchette 
Austrian Rail operate under the Brand of “Nightjet” a good network across middle and western Europe 

Hello Seawolf and thank you for reply!

so for example, I am thinking about a night train from Berlin HBF to Malmö Central on 5/16 (2058 departure in Eurail app) and would like to be able to sleep or at least have my 1st class Eurail ticket seat reserved and not pay full ticket price since I have the Eurail pass.

So you are saying to not trust the Eurail trip schedule and always check the local schedule?  

Yes, all regulars answering here do that. They also have our very own experiences!

THIs train you mention is in fact a kind of private enterprise and they do offer small discounts for passholders. You can book the supplmt for seat/bed on their own site: snalltaget (that is swedish). It runs on to Stockholm and as the sea is in between in fact it makes quite a detour-via Hamburg-Flensburg-Copenhagen.  Nighttrains are in fact not ever present and most do not have specific 1st seats-often only 2nd, as they assume those who can pay so much for 1st will want a bed. Most local/regional trains also do not have 1st cl anymore-this differs per country. These trains are never REServed though-they work just like the metro or LIRR/CalTrain.

OH-this is EUR so we do the logical order always: day-month-year. This often confuses US-newbees.

This train offer just Couchette or seats :/  last year it was obligatory to reserve a whole compartment due Covid not sure if these rules apply in 2022 too :/ 

Yes the websites of the traincompanies itself are more actual. 

That's correct. The planner app does not get enough updates to be reliable. Use the operators’ or national planners/apps; for international planning, the German railways planner is a good choice (although the night train Berlin - Malmö - Stockholm seems to missing there).

To book the night train Berlin - Malmö with Eurail, go to the Snälltåget website (the operator) and use the promotional code "EURAIL”. You'll see a fare of SEK 199, which is for a seat, but in the next step, you'll be able to change that to "shared compartment” (a berth in a 6-person compartment) or "private compartment” (a 6-person compartment for yourself or the group you're booking for).

Unfortunately, this train doesn't have real sleeper coaches.

I spoke with a Snälltåget representative on the phone. Here's some information:

* A berth in a shared compartment is possible to book. Due to a bug in their booking system, no interrail discount is currently available for this, and they don't know when it'll be available. They are not even able to book it if you call them. According to their website it's supposed to cost ~38 EUR (399 SEK) but currently you're forced to buy the normal full price for ~117 EUR (1249 SEK). This Danish travel agency claimed in 2019 to be able to sell the ticket at the discounted price. 

* 6 berths in your own private compartment is also available. This is possible with the INTERRAIL discount code on their website yielding a price of ~217 EUR (2299 SEK) 

* A seat is also available with discount as @rvdborgt mentioned

* Take-away-breakfast costs 6,5 EUR (69 SEK)

@NextDeparture the normal fares vary but I now see that the shared compartment displays the same price with or without the INTERAIL or EURAIL promotional code.

Did Snälltåget say what you should do now if you want to book a shared compartment with Interrail or Eurail? They should at least put a warning on their website and advice what to do.

@rvdborgt they told me to buy a reservation that can be refunded and hope that the bug is fixed before my departure, so you can refund the ticket yourself and buy it again using the discount code. 

Hm. That is hardly acceptable. They promise a pass fare so they're obliged to offer it, regardless of how their website works. I'd indeed book a refundable ticket but if they don't fix it in time, I'd ask for a refund of the difference, which they would be obliged to give.

@rvdborgt I requested a partial refund over email, let's see what happens :-) 

Do let us know what happens!

It is now possible to use the INTERRAIL discount code for a shared compartment. I refunded my ticket (since I bought a refundable one) and bought a new one with discount. 🎉