On my side the regex code is twice as slow as a for loop (2526 ms vs 1149 ms).

Thanks better late than never on the reply :)

I have tested it and it is correct here and in other solutions too)

I do a foreach loop for 1_000_000 repetitions of the "yacht is the sea with a man in the sky" line discussed above, and compare it to regex.
Results:
1280 ms - for loop
1137 ms - regex
the for loop loses an average of 100 ms. LINQ is slower - 1809 ms

Summary: regex is the fastest and most obvious - really best practice)))

I agree.
I would replace
str
with
str ?? ""
assuming that it can be possible to receive a null value, ex. a failure in reading a troll's comment...

I'm coming from Javascript. How C # is different. I will have to study hard. JS is very abstract, but C # ... I will suffer a little, but I like it.

For such simple algorithms, I would argue the opposite as best practise: for loop > LINQ > Regex

Regex is overkill for anything.

If it's a very simple parse, like this, you'll get better performance and code that's easier to read by just writing it out imperatively. If it's a complicated parse, you'll be less likely to run into bugs, and have code that's easier to read, by using a proper parser DSL such as ANTLR. Regex isn't particularly good at either case, and its complexlity is extremely high. The "now you have two problems" joke exists for a reason.

Trim replaces the spaces only in the beginning or end of a string. It combines "TrimStart" and "TrimEnd".

What is better for performance, built-in string methods or Regex engine?

I thought Trim erase all spaces!, Does this only trim the two sides?

gave this a bestPractice ... but how would I know? I am beginner... is it BP?

penetrating

Is regex an overkill for this one? Just asking because I'm not really familiar with regex.