I don't think anyone here can advise you with any certainty, sorry. It's impossible to say and may depend on where you're planning to go.

At the moment everything where I live (Munich) is open as normal to fully-vaccinated people. The Christmas Markets are still due to start next week. But in other towns in Bavaria and across Germany it's worse than here, there's still a pandemic, we are in a current wave of infections. Rules can still change with very little notice and very locally. I can't see that December will be any different, and may be worse.

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