Why HIMYM TV ending is Ted's dream?
I believe that "How I Met Your Mother" TV ending is a dream
The main reason - the ending speech is voiced by "young Ted".
In all other episodes the story is always told by "old Ted".
And only in this finale it is suddenly told by "young Ted".
So for me the only possible explanation - it's a dream.
The dream after which Ted wakes up with Tracy in his heart and Robin in his mind. Then maybe he thinks about his life, speaks with Tracy, with Robin. He realizes that now his feelings for Robin are mainly nostalgia about "being young and stupid". As well as his stories he keeps telling.
Eventually, he decides to feel grateful for that time, but live for today, making new stories to tell his grandchildren.
"Life only moves forward".
And then we can watch the DVD real ending.
Suddenly - it is voiced by "old Ted", making it the only real ending.
© Music: The Solids (feat. John Swihart) - "And There She Was"
"For Robin, Ted had to make it rain. But for Tracy, it was already raining." (comment by "Li Li" on YouTube)
More on the DVD vs TV endings (most in Russian, some in English) - https://www.notion.so/How-I-Met-Your-...