What is the Christmas/New Years celebration like in Vietnam?  

In Vietnam, they celebrate Tết which is the new year for them and it falls on January 22nd in 2023. As for Christmas, it is celebrated the same with family, dinner, and lights. While most people in Vietnam fall under Buddhism and the Chinese philosophies of Taoism and Confucianism in terms of religion, roughly 8% of the population is Christian/Catholic and they enjoy the festivities just the same. 

I think the celebration of the new year is a big deal but they don't celebrate it the same nor on the same day even. Christmas, you will see festive lights here and there mostly in the bigger cities but typically not as much as you would see in the west.

Well, it's a mix. We don't really have a Christmas tree in our homes unless we're fortunate enough to buy it but we do have a lot of Christmas decorations up around town. We also have a lot of New Year celebrations, like parades and fireworks. There are lots of lights and decorations everywhere, and there's a Christmas tree at the mall. Usually people go to the mall to take photos or to any of the decorations that are in public places in the city.

Vietnam is 80% Buddhist, to which you must had a religion specific to each of the 52 minorities. So, out of 99 million people, there are only about 2 million catholics, but fervent Fiathful. For them, Christmas is the biggest after Têt, with cathedral and churches filled up for the Midnight Mass; Funny thing: in Sapa, populated mostly by Black H'mong people, that mass is in Vietnamese and then in H'mong.

The country benefiting from an intense development (6.25% in 2022 !!!), the Vietnamese have more and more money, so they go out and travel ; since several years, the non-Catholics have discovered that having fun for X'mas is an excellent idea, so, they go out to restaurants and celebrate what they do not believe in with a lot of food and ruou (rice alcohol)

I think most of what I would have said has already been addressed. It is a celebration for many but not quite like Christmas in the west. I would compare it to Thanksgiving in the US. It is just taken as a day to have a family meal and spend time together. 

Christmas is a secondary celebration, the big deal is the new year which happens at the end of January every year. Both are celebrated but one to a much lesser extent. You will be among the minority celebrating Christmas. 

Not everyone celebrates it, just the same as anywhere else in the world. It depends on locations and family traditions. I know some Vietnamese people who don't celebrate either.