Interrail is not valid in Ukraine or Russia. You will need a ticket that is valid from the border of the last country in which the pass is valid, or earlier, depending on the train.

It is still useful to have a complete timetable, even if Interrail is not valid everywhere.

@Laurie Roff  for Russia you get a small discount for the Trains from Helsinki to St. Petersburg and the Nighttrain to Moscow besides this one Route Interrail is not valid in Russia :)

for Ukraine you can use a special offer of Austrian Rail from Vienna via Budapest to Lviv or Kiev besides this one Route there is no advantage in Ukraine with Interrail but train travel in Ukraine is pretty cheap and you can book many domestic Routes online at the page of Ukrainian Rail :)

did back in 2019 Berlin - Kosice - Regionaltrain to Chop (cheaper the direct coach from Kosice to Lviv - Kiev) From Chop via Lviv to Odessa and then via Tiraspol - Chisinau to Bucharest :)