I overlooked you question, well …
In winter like in France things can be nice or not, if you are not into cold, rainy, snowy weather better not, if you do not care about the weather, then come whenever you want.
Outside activities are either not possible or only possible in the winter. Winter sports actually are most in the Alps happening in other regions the climate change is happening and there is no snow for sure.
Because it’s often rainy and cold outdoor activities aren’t that “nice”, of course there are indoor activities, but not every region/town has it, like bouldering, even swimming, skating, …
Some tourist attraction are even closed, because they are old and the constant change of air and temperature can’t be regulated. Especially some castles might be closed or have shorter access.
But what do we have in winter that we do not have in summer?
Christmas markets, skating rings outside/indoors (some indoors place in the sports areas may be operating all year but if they are then open for public, I do not know).
Carnival - there are sessions and there are street parades, depends heavily on the region you go to, some don’t do it at all, other regions seem to go full force the biggest example Cologne.
Carnival starts in autumn November 11 at 11.11 am.
This year it was still practiced but if it’s possible next year, there are already a lot of cancellations. Depending on the Christian calendar it ends in the night to Ash Wednesday as fasting before Eastern starts. It’s also called the 5th season in Germany.
A nice one in Advent, poor people, children were allowed to improve their living a bit by given food or whatever. On 3 Thursdays they would go around the houses when sun was about to set and sing they would sing Christmas carols and would in return get apples, pears, bacon or even some pennies in return.
One that is my only fixed DIY project for the year, if I don’t get to do anything at all the Adventskranz is the one I will do it myself and you will see the Adventskalender I mentioned earlier in a comment.
The oldest Christmas Market in Dresden where you get the traditional Dresdner Stollen
In Germany the 4 Advents Sundays are not meant for shopping, so no open Sundays for the regular shops allowed, only on the Christmas Markets you can buy something. Normally Saturdays the shops do extend their business hours, so everyone can find their Christmas present in time. Be aware that most shops will close earlier on Christmas Eve either at noon or in the evening. Christmas Eve is no holiday but the following 2 days are as the are called 1. and 2. Weihnachtsfeiertag, yes we kind of count them and I know that in English the 1st one is Christmas Day and the 2nd one Boxing Day.
What do Germans eat on Christmas, well everything is possible? Traditionally you would go for a filled goose, but Wiener Würstchen and Kartoffelsalat are common as well.
(wiener and potato salad).
Of course, we would do a lot of cookie baking, if we have the time, if not there are a lot of choices to buy, my favorite to buy are small Lebkuchenherzen( ginger bread hearts filled with apricot jam. My favorite to bake are probably Mandelherzen/Almond hearts.
The exchange of gifts in Germany is traditionally on Christmas Eve, now you know why shops do not open that late, so most people can be at home.
And a lot of Germans who do not go to church over the year will go on Christmas, so one of the days you can expect a filled church is this one. I was never to keen of it, I am not a friend of standing too close in churches, and I was always the polite one letting the elder ones sit, so I would stand in the back for an hour with a bit of luck close to the door catching a cold. My mothers wish was ones to go to a Christmas Mass as the pastor retired so for the last time we went there, and he made it tradition there to switch off the light at the end of the mass and only with a few candles and the illuminated Christmas Tree we would sind Stille Nacht Heilige Nacht/ Silent Night Holey Night.
But if you thought this is it for the year no more food, well there is still Sylvester to come.
Similar to Christmas Eve shops will close earlier.
But for Christmas there are two option you will be at home or you will go out.
At home with family and/or friends either you cook a feast or make a big buffet, some do raclette (orignal from Swiss), or fondue (original from French/Swiss … many countries have different versions). You might just go out in the streets to celebrate that is possible in some cities or communities.
And at midnight there will be fireworks and everyone will wish the other a Frohes Neues Jahr/Happy New Year.
In the morning depending on your state you can eat herrings or Neujahrsbretzel, this pretzel is normally bigger than the regular German pretzel some may know, it’s made of a slightly sweet yeast dough and you would eat it with butter, honey, jam …
The herrings are often made a day or two before eaten, because the taste and tenderness will increase after being covered with onions, apples and a lot of cream.
Are we done with everything regarding Christmas in Germany? No!
There is still the 6th January the day of the Three Holey Kings when the kids from the catholic parish go around. These you must “order” them to come, so they can organize better. Sternsinger (star singers) go from house to house and sing to get money for children in need around the world.
So this for now @piranna I hope something interesting is there for you.
I am sure I forgot something but there are others so maybe they will fill in.