Democracy seems to have been saved from the threat of MAGA.
I think I know the way you mean that, and agree - for now. But also, there are Republicans conceding elections, and so far, none has thrown a Trumpian fit about losing. That's an encouraging trend for democracy - a respect for the peaceful change of power.
Can/should Democrats be openly patriotic?
They are, but it sounds like you mean something other than love of country and its principles. Can you be more patriotic than Joe Biden or Merrick Garland? The question is when the Republicans will show some patriotism beyond not tantruming over election losses. Cheney and Kinzinger get gold stars, but most of the party, the MAGA contingent, are enemies of Americanism - democracy, egalitarianism, rule of law, and church-state separation. Do you stand for those? If so, you are patriotic. If not, you're not. If you actively work to thwart them, you are as anti-American as any foreign enemy such as Putin.
Is it acceptable (or even encouraged) to be a Democrat who believes the US is the greatest country in the world?
Why would that matter? What if they thought it was the third or seventeenth best country? A patriot is somebody that wants his country to be the best IT can be. This isn't too different from the love of a parent. Mom wants little Susie to be the best person she can be, even if some others can go further.
They don't seem to be. More like they believe we should be ashamed to live here.
I'm an American who was unhappy with American life, retired earlier than I had originally planned, and traded that life in for a different kind of life among a different kind of people in a different culture - a change few of us expats here in Mexico regret. Most of my social circle is Canadian and American expats, and the Americans are mostly liberal, so there's really no MAGA presence in my life anymore. We had no mask tantrums during the pandemic, and I never once heard the word tyranny with regard to mandates. Religion isn't toxic here, and people aren't being shot up in schools and malls. My last American residence was rural Missouri, which is MAGA country, and which was already an undesirable place for a liberal to be in the Bush years when I left.
I could have stayed in America - perhaps returning to California - but why? What does America have to offer a liberal retiree? Freedom? That's the usual answer. My fellow expats that return to the States do so for family support if they've become infirm, or for Medicare benefits not available abroad, but never for more freedom.