Which is correct, and if both are correct, which one is better and what would be the difference in meaning?
It is only that last year that I've been taking it seriously.
It has only been that last year that I've been taking it seriously.
The meaning I want to convey: In previous year 2019, I started to take learning French seriously and I'm still taking it seriously during this year too, 2020. However before 2019, I wasn't taking it seriously at all.
Update : That in that last year in both of my sentences is meant as an adjective (eg. This year/that year) not as a pronoun that has to be followed by a clause with at least one verb and one subject. And I intented to use that because for me 2019 is like a far away object that I'm pointing at from far away.