It's not anti-democratic to force candidates to abide by existing law.
For example: AOC couldn't run in 2020 because the Constitution states you have to be 35 to be President and she would not have been old enough.
That's not anti-democratic, that's the "you must be this tall to ride this ride" rule.
For the same reason, removing an insurrectionist from the ballot is not anti-democratic. They've proven they can't be trusted and so aren't qualified for office, and the 14th Amendment disqualifies them.
You vote for representatives that make laws on your behalf. Everyone has to follow those laws. If you are a president and also a traitor, you will run afoul of those laws. If the law says you may not run for president if you break it, then that is what it is. Democracies can have laws and still be democracies.
So far he hasnt been convicted of any treason, or any other crime. Right now its entirely one party subjectively deciding to deny candidacy to the opposition party, as Russia and North Korea both do.
We ALL saw that traitor incite an insurrection in an attempt to overthrow the United States, and good thing the 14th amendment does NOT require a conviction to keep a traitor off the ballot.
Spare me the Russia North Korea bullshit, the anti-americans are the ones trying to destroy democracy and anoint their rapist god as king of America. Just like Russia and North Korea.