How do I share calendar between two users on MacBook Air M1 ?

Where did you see these "instructions".

From reading your query I understand that:

• You have one Mac
• You have two user accounts on your Mac; one for yourself and one for your wife.
• Each user account is signed into iCloud with different iCloud/Apple accounts
• You have the basic free 5GB iCloud plan

You can share your calendars from each of your iCloud accounts and you don't need one of the paid iCloud+ plans to do it. When you make a change to the calendar in your Mac user account, your wife will receive these changes to her calendar when she opens her user account.

See the support video

Apple's support video

on how to set this up. The example is from an iPhone but it is the same in the Mac calendar.

You will need to do this for each of the calendars you wish to share in the app. One might suit you or you might want several.

Also investigate the Family Sharing service.