As per the article https://support.apple.com/en-in/guide/reminders/remndbeda47c/7.0/mac/10.15
Mark reminders as complete
In the Reminders app on your Mac, do any of the following:
- From a notification: Click Complete in a reminder notification when it appears in the top-right corner of your screen.
- One reminder: Select the circle next to the reminder’s name.
- Multiple reminders: Select the reminders, then select the circle next to one of the reminders (or tap in the Touch Bar).
If a reminder is set to have repeated notifications and you mark it as complete, the reminder for that day moves to the completed section of the list. The reminder for the next repeat date appears in the reminders list.
Read this article also https://support.apple.com/en-in/guide/icloud/mmc0cd794a/icloud
You can create and manage to-do items and organise them into lists using Reminders on iCloud.com. You can also share reminder lists with other iCloud users.
Changes you make to reminders and reminder lists on iCloud.com automatically appear on your iPhone, iPad, iPod touch and Mac when those devices have iCloud Reminders turned on.