I have used the Excel/Word/Keynote formats with iWork and it’s okay. MS Office is the de-facto standard format and recognized by Google Docs, OpenOffice, and of course MS Office.
I don’t think it’s a truly open format like ODF, but you can be sure it’ll be recognized everywhere for a long time.
Very few people will be able to use it: only iPhone 15 Pro and higher. Most users won’t have a capable phone until their next upgrade in 1-3 years.
Hopefully by then they’ve caught up to where Anthropic, OpenAI, and Meta are today.