OnlyOffice is designed from the ground up to be more compatible with MS document types.
I've been using it for about a year now and haven't yet experienced any compatibility issues with MS office documents.
I would guess that business excel is going to be pretty basic. You're going to learn how to create business reports like P&L statements, depreciation schedules, simple profit forecasts, and so forth. All of which should be totally possible in OnlyOffice, or LibreOffice for that matter.
Powerpoints and Word documents are even more basic and will be totally fine in OnlyOffice. I'm literally doing a presentation on cyber security for a multi-million dollar business in a few weeks that is done completely in OnlyOffice and with 100% open source software and assets, even the fonts.
If you must use MS Office for some reason, use a copy on your University's computers.
Don't fall for the propaganda, FOSS solutions like OnlyOffice and LibreOffice will work fine for 95% of people out there, probably more honestly. I used OpenOffice then LibreOffice all through late Highschool and my University studies, wrote scores of papers and a bunch of presentations, never once had any problems with features not being enough.