Reverting Aptos +body/+headings font back to Calibri, or using any other font

At some point in the last couple of days, the default +body/+headings font on my copy of Office 365 changed to the Aptos font. I honestly find it a bit hard to read, and I'd rather choose my default body font from a choice of whatever fonts I have installed. Failing that, I'd take Calibri again. The Aptos font reminds me a lot of

Since this affects all Office products, I can't say go into Outlook and change the stationery fonts; this doesn't impact the Reading Pane. It also wouldn't impact say Word, where I'd have to come up with my own document template to override the change. It doesn't seem to be a registry edit or template file edit, either. Is there a spot that the Aptos font can be changed?