In any case, the non-voters are OK with whatever party might win, because otherwise they should have made their vote or created a political party that might be agreeable to them.
Also, in practice, no, you cannot make a political party in Greece. There's a country-wide threshold of 3% that you need to exceed to get into the parliament. A lot of well-organized parties struggle (and often fail) to exceed it. So even if you get 100% in an electoral district, you won't get its respective parliament seats. In fact (IIRC the tidbits of the election law), you will be making the first party stronger (and I don't mean by depriving votes from the second party).
This is not unlike other Western democracies. But this is essentially a design to cull any grassroot movements. Not very democratic.
You can quibble about whether a 3% threshold is "democratic" or not, but for all practical purposes if your movement can't get 3% you stand no chance of getting your policies enacted.
One can still fault them of course, but it is a distinct category, and it is not at all a clear sign of consent, if even the active choice ever was.
That alone is pretty un-democratic, no? Certainly politics is a world where it's hard to find an ideal situation pretty much ever, but I think a democracy where a third or more of eligible voters don't want to support any available candidate... that doesn't sound particularly democratic.
The US with its two-party system suffers from this problem, and it's a very bad one. There were more eligible voters in our 2024 presidential election that didn't vote at all (89M) than there were people who voted for Trump (77M) or Harris (73M). It's pretty messed up that more than a third of the electorate was so dissatisfied with their options that they didn't cast a ballot at all.