Start your own there are so many ways to combine all 33 countries :)

Please let me know if you got one.

As not all countries are well connected it quite hard
but you could start Germany - Copenhagen - Gothenburg - Oslo - Trondheim - Östersund - Stockholm - (short cut ferry to Finland) or Stockholm - Lulea - Tornio/Kemi - Helsinki - Ferry to Tallinn - Tallinn - Riga - Vilnius - here is currently still a bus needed to Poland - Poland - Warsaw - Krakow - Ostrava - Kosice (SLovakia) - Budapest - Bucharest - Istanbul - Sofia - here a bus to Thessaloniki - Athens
 
North Macednia , Serbia and Montenegro are currently hard to reach (maybe leave them out)

Athens - Patras - Ferry to Italy - Venice - Trieste - Ljubljana - Zagreb - Vienna - (passing through Liechtenstein) to Zürich - Milan - Genoa - South coast of France - Barcelona - Mardrid - Badajoz - Lisbon - Porto - Vigo - Irun/Hendaye - Paris - London - Holyhead - Dublin - Belfast - Liverpool  - Glasgow / Edinburgh - London - Brussels / Amsterdam

From Amsterdam to Luxembourg :)


It´s just a idea and the route combinations are endless have a look on the map and just start :D
 

From Genova you ALSO pass MOnaco! 

Make a quick side tour-spend the extra for frecce=hispeed, from Milano to Roma (eternal city+ PLUS Vaticano-maybe even see the pope!). Or even better: via Roma coming off ferry from GR.

(PS: yes, I´ve visited all countries of EUR-even though San Marino only a few hrs), incl those that do not accept the railpass, like Ukrayna (in happier times of course)/Byelorus/Moldova. But that was over the span of much more as 20 yrs)

Reaching PT and coming back is very time-consuming, if you do not follow GRethaś footsteps overzealous, simply fly from somewhere in PT till Paris or direct BE/NL or so, or UK-if booked smartly less as 40€=perhaps even less as the mandatory extra REServations you need to make by train.

There are 100s of such blogs and as you are-selbstverstdl-denn die alle sind das ja auch-deutsch- can easily read them. Also try the old site of rail.cc (used also to have a quite informative forum like this, aimed at poor bekpekkers, but has merged due to corona with raildude=mainly for USAers.