"Microsoft is already facing complaints on multiple fronts: Slack took exception to it bundling Teams with Office 365"
You are free to NOT buy or use Office 365, and the fact that it includes a 'bonus' teleconference app, that has PLENTY of competitors, does not force you into buying into Office 365. You have a choice as Office 365 is *not* bundled with Windows, you must both choose to install *and* [pay] subscribe to it in order to get the (added) Teams functionality.
No case.
"Nextcloud filed papers with the EU over Microsoft bundling OneDrive with Windows"
This is stickier. You still have the option of not using OneDrive but legal precedent shows that law makers consider that a form of 'lock-in collusion' by pressuring users to stick within the granted ecosystem (strange how Apple gets more leeway in that field...).
Nextcloud may have a case here so I am not going to volunteer a judgement outcome.