A standout feature in Office 2021 for Mac is:
By 2021, Mac OS X Lion (10.7.5) is over a decade old. Microsoft Office 2019 and Microsoft 365 (formerly Office 365) do not support Lion. To use Office on Lion in 2021, you must rely on older, compatible software with workarounds for security and cloud connectivity. microsoft office for mac os x lion 1075 2021
Even if your Mac is stuck on Lion, you could use Office Online in a browser for basic co-authoring — it works on older macOS via Firefox or Chrome (where still supported). A standout feature in Office 2021 for Mac