Holidays in Europe - where to go?

With the time you have I would stick with Portugal since it is sunny and has a beautiful sunset setting on the Atlantic.
You can get some itinerary ideas:
https://www.ricksteves.com/europe/portugal

I would opt for Lisbon as the weather should be milder than Germany and not as wet as northern Italy. It fits your food, drink, museums requirements. Lovely people and good transport links.

Congratulations on your nuptials.

Keep in mind, you have a short (actually, a very short) trip. You will need to be careful to limit the scope of what's doable in that time (you will want to minimize the time you spend getting around). Also keep in mind that you will be there during the holidays (looks like you will arrive on Christmas Eve, your first full day there will be Christmas day; you will also be there on New Years Eve and New Years Day...that will effectively wipe out 4 full days out of an already short trip, do the math...). Many things will be closed and/or have limited holiday hours. On the plus side, you'll get to experience a bit of those holidays from a European perspective (to the extent that a visitor can).

I agree that of the places you mention, Portugal would be my choice.

(looks like you will arrive on Christmas Eve, your first full day there will be Christmas day; you will also be there on New Years Eve and New Years Day...that will effectively wipe out 4 full days out of an already short trip, do the math...)

Not really. I 've spent 5 New Year's eves/days in Europe including in Paris, Amsterdam, Orvieto, Collioure, and Seville.
New Years Eve you site see in the day and party ringing in the New Year in a club (depending on what you like) with the locals who will all be out.
New Years day you sleep in late like everyone else and then can go to the beach in Portugal (we had a picnic at the beach on the Atlantic Ocean watching the sun go drinking a nice wine in Cadiz in neighboring Spain on New Years day 2019).
A full day of quiet is fine spent it in a nice setting on the ocean with the one you love.

I never pay good money to visit Europe in the Winter. We lived in Germany for four years and got so tired of those long cold nights (at Christmas time in Germany it gets dark at 4:30pm).

Still, for a honeymoon, you want somewhere romantic. Florence and Venice are romantic places and Italy is loaded with museums.

Switzerland in Winter may involve snow.

I would save Portugal for another trip.

My wife and I went to Belgrade, Serbia recently and we were pleasently surprised by this hidden gem. Everything from the cuisine to the architecture was stunning, as well as the nightlife (albeit we're a bit too old to party). Nevertheless, the city is as rich in terms of cultural and recreational manifestations as any other European capital, with the exception of a lot of places being open almost 24/7. I don't know about hotels, but the accommodation was pretty cheap compared to the surrounding countries (we stayed in an AirBnB, but we booked them for cheaper from apartmanibeograd.com), let alone the EU countries. From museums to medieval fortresses and monasteries, Serbia is really rich in terms of culture. The guys who were our hosts were kind enough to show us around, and we got to experience Belgrade the way a local would. The people are very hospitable, and the city never sleeps. I highly recommend it.

Come a few days earlier and you can enjoy Christmas Markets. Most generally close Christmas Eve, however the one in Budapest stay open until January 1 (without the food stalls).

There will be a lot closed 24, 25 and 26 of December and on New Year Day but I've been to Europe a few times during those periods and still find plenty to do.

Also, get ideas here but be sure to confirm reality. The weather in a particular location is one thing you can easily check.

Spain may be a good choice. It's warmer in southern Spain and Christmas lasts from December 25 to January 6. In Spain, January 6 is the big day; the rest is essentially the twelve days of Christmas.

Barcelona is the least religious area of Spain, it's a great city but not likely to celebrate Christmas to the same extent as the rest of the country. Most of Northern Spain gets very cold. I'd recommend staying further south (Seville, Granada, etc.)