Gamer your grammar is okay. I have a few comments tho, which might bore you to tears
Winter holidays were wonderful.
A lot of interesting things happened during this period.
Okay but wonder Gamer if you might mean "those periods"
…duering which we encountered many interesting events, or
Many interesting things happened (back) then
December 30th we finished the study.
Okay tho I'da said
We completed the study Dec. 30
I was invited to a New Year's Eve.
We usu add "party"
Usually my morning started with a delicious breakfast and charging.
Then I often went to the rink.
…..after which I often went skating
In the evening, I was sitting at the computer.
You don't want that comma. Also this one leaves us unfulfilled
That evening as I sat before my PC,…. or
In the evening you could often find me sitting at my Apple Mac
Evenings I sat at my computer (PC, Mac... )
Sometimes I read a book.
Occasionally I read a (an entire) book
It was great and I had a good rest
It was a great read, (at the same time) proving restful or
It was a great read, after which I had a good rest
Many interesting things happened during those wonderful winter holidays. Usually upon such an occasion my morning starts with a delicious breakfast, then after changing into something comfortable but warmer I was off to the (local) rink.
But this time on Dec. 30, just as we finished the study in question, I was invited to a New Year's Eve party (wingding) that proved (turned out) really fun. Then having judiciously remained fairly sober, later in the evening during my usual bout at the PC I was sitting at the computer when I decided instead to read a book, a great idea and a good rest
Forgive an old guy Gamer who has participated in that sort of stuff (editing, not partying) for many decades before retirement