I mean I know there's "Year of Rail" and all that, but that doesn't seem to translate to anything more than words right now. (Like - no actual trains you could book.) The number of night trains has decreased over the last couple of years. It'd be nice if that trend would be reversed, but that will take more than proclaiming a year of rail.
https://www.nightjet.com/en/reiseziele/frankreich
I could book a seat on that train for tonight. AFAIK ÖBB (re-)started that line earlier this month.
Also, the overnight train connection from Vienna to Hamburg is really convenient. I took it some years ago. If I recall correctly, the train departed at around 20:45 and arrived in Hamburg at 6:45.
France brought back a bunch of national night trains. ÖBB brought back Paris-Vienna, and they have more plans. Sbb brought back Amsterdam-Zürich, also planning train to Barcelona. Sweden wants to get back into Europe (not successful yet). Poland wants to connect west again.
There's a bunch of private endeavors: berlin-Malmo-stockholm is running more often, there's a startup starting a Prag-Berlin-amsterdam-brussels service in spring '22, another older company started Alps-munich-hamburg-coast this year. There's a startup that announced all sorts of impossible routes out of Paris. Another announced brussel-berlin.
The bottom on night trains was 2017. Jon Worth probably has a bunch of opinions about that.
SJ (Swedish State Railways) won the Swedish government's tender to provide night train services Stockholm - Hamburg starting in summer 2022.
Hopefully it's in service now, but last time I looked it up, there were still issues.
And to the original point that "at least in Europe there is a push to bring back overnight trains as an alternative to carbon-intensive flying", there is this from 5 days ago: https://www.cntraveler.com/story/europe-is-undergoing-a-slee... which leads with the Caledonian Sleeper, and mentions others such as the new Paris-based Midnight Trains, the revival of the Trans-Europe Express, Czech-based RegioJet, and ÖBB's Nightjet.
The fun part is: Finland now requires a proof of vaccination to enter but doesn't recognize Russian vaccines, and vice versa. So as a Russian, if you really want, you could get Pfizer or something in countries that would let you enter with a PCR test or recognize Sputnik V, and then you'll have a EU-worthy vaccination certificate. And that's on top of still needing a Schengen visa. So I really don't know who these trains are for right now, besides like 5 people I know who did that exact thing above.
The link states that two daily Allegro services have been re-instantiated. Due to Russian legislation, using the service is only possible for Finnish and Russian citizens. It is true that EU and Russia do not recognise each other's vaccines, but a negative test result allows travel. Russia seems to require a test result in any cases. It is possible that Finnish government starts requiring a negative test result on the Russian border, too, due to the omicron breakout.
But then even if you are admitted into the EU, you would be considered non-vaccinated for any place that requires a proof of vaccination, and from what I heard there are many such places.
p.s. don't tell the kids, but the best thing about Finland: reindeer steaks. Who knew Rudolph was so tasty?
That's why I hold my expectations really low about international train travel. With airplanes it's actually much simpler, since air travel acts as a network and routes around failures (such as, even if you can't get from country A to country B directly, you can usually go transitting via country C without any restrictions).