https://www.politico.eu/article/robert-fico-threaten-cut-ukraine-electricity-supply/
tl;dr:
Northern Hungary and Hungary was buying gas from Russia. The goods were flowing in pipes through Ukraine. Ukraine and Russia had a deal: Ukraine gets free money just to allow the flow of gas through the pipes over the country. The pipes were there since the Soviet times, so they literally had to do two things: pocket the money and nothing else.
This contract of transit expires on 2025 January 1st. And Ukraine decided not to renew, which means no more gas through the pipes.
Ofc the transit is good for both EU countries, and I suspect Fico and Orbán decided to make some noise, this time the turn was on Fico.
I doubt anyone will care, but that's that.
Note: a new transit deal could be part of a peace negotiation.

It the past couple of years our govt. made quite an effort towards the Balkans, Serbia and Bulgaria, to secure gas via Turkey and the Turkish Stream, negotiating trade deals and helping out with migration, perhaps more. I don't know if it's enough, I mean the amount of gas.
We have no shores and just a token port in Croatia to receive LNG ships, so we are reliant on pipes no matter what.