I am colouring some musical scores which need a few notes and symbols coloured to convey specific situations.
The scores are being created in Avid Sibelius 2021.2 (latest version) and exported as SVG page by page. I then open those SVGs in Illustrator 2021 (as of today no update available) and start the colouring process.
The font being used for the text is called Academico and should be an open source to download.
Finally, I am on macOS Big Sur 11.2.1 and this bug I'm about to report seems not to reproduce on Windows.
Please download this SVG and check in Finder that the preview shows all text in Regular or Bold and that there is no Italics (as it should). Then open it in Illustrator and, at least on my system, it shows all Bold correct but all Regular as Italics. The whole experience can be seen in this video.