So I've encountered links to this Meduza publication on Politics.SE, which states:

In 2022, when the city was the site of a months-long battle between invading Russian forces and the Ukrainian army, 90 percent of Mariupol’s apartment buildings and 60 percent of its houses were destroyed, according to a UN report.

This is mirrored by another article saying the same (in Russian), to confirm that it is not a fluke but a claim made in earnest:

Во время боев за Мариуполь в 2022 году было разрушено 90 % многоквартирных домов и 60 % частных домов, сообщали в отчете ООН.

The problem with both of these claims is that they both reference the same OHCHR report, which states that

We assess that up to 90 per cent of residential buildings have been damaged or destroyed, as well as up to 60 percent of private houses.

This report does not contain actual evidence that all 90% of these buildings were actually destroyed (or completely damaged beyond repair, which would count as destroyed), but it does not disprove that claim explicitly either. So I would ask for sceptics input to answer this question.

So I've encountered links to this 2023 Meduza publication on Politics.SE, which states:

In 2022, when the city was the site of a months-long battle between invading Russian forces and the Ukrainian army, 90 percent of Mariupol’s apartment buildings and 60 percent of its houses were destroyed, according to a UN report.

This is mirrored by another article saying the same (in Russian), to confirm that it is not a fluke but a claim made in earnest:

Во время боев за Мариуполь в 2022 году было разрушено 90 % многоквартирных домов и 60 % частных домов, сообщали в отчете ООН.

The problem with both of these claims is that they both reference the same OHCHR report, which states that

We assess that up to 90 per cent of residential buildings have been damaged or destroyed, as well as up to 60 percent of private houses.

This report does not contain actual evidence that all 90% of these buildings were actually destroyed, but it does not disprove that claim explicitly either.

Were 90% of Mariupol's apartment buildings destroyed?