I need free alternative of Excel in Mac Os. I know that there is Open Office, but I am not sure if it is even supported anymore.
By adding a table to Numbers, you can use Apple's replacement instead of a third party's. Numbers is free for anyone with an App Store account (which may require registration and a payment card - but no charge whatsoever).
Numbers is supported and designed to replace Excel for the majority of Mac users.
I use LibreOffice which is a really good alternative for MS Office. I've been using it for a couple of years now (on my Ubuntu earlier, now on MacOS).
If you need an online version of Office I recommend GoogleDocs. Full document edit history, collaborative editing, and ease of sharing.
Excel is available for free from Microsoft as part of an entire suite of products via Office Online.
There's no need to search for a "free" Office alternative when Office is available free as a service. You will just need to create a Microsoft account to use it.
The benefits over the alternatives:
No software to install (i.e. LibreOffice/Open Office). All you need is a web browser.
Native Excel as opposed to "XLS compatible" (which is never really fully compatible)
Free 5GB OneDrive storage included with your account
Fairly standardized UI across all devices (macOS, iOS, Windows, Android)