Breakdown of Фрилансер написал мне насчёт портфолио.
я
I
написать
to write (perfective)
насчёт
regarding, about
фрилансер
the freelancer
Questions & Answers about Фрилансер написал мне насчёт портфолио.
Since насчёт requires the Genitive case, why doesn't портфолио change its ending?
Because портфолио is an indeclinable foreign loanword. Like other borrowed nouns ending in -о or -и (such as метро or такси), it never changes its ending regardless of the case. It is grammatically in the Genitive here, but the spelling stays exactly the same.
What is the difference between using насчёт портфолио and just saying о портфолио?
I sometimes see this spelled as two words (на счёт). Why is it one word here?
насчёт (one word) is the preposition meaning 'regarding'. If you write it as two words (на счёт), it literally means 'onto the account', as in depositing money into a bank account (положить деньги на счёт). Since the freelancer is writing about the portfolio, it must be the one-word preposition.
Why use the perfective verb написал instead of the imperfective писал in this sentence?
The perfective написал is used because this is a single, completed action that produced a result (you received the message). If you used the imperfective писал, it would imply he was in the process of writing to you, or that he wrote to you repeatedly over a period of time.