Reminders sharing not working on iCloud or iOS
If I share a list in Reminders, it is not shared. Nothing happens. Problem occurs only on iOS and iCloud.com.
It works when I share a list on Mac.
iPhone SE, iOS 12
Using an iPhone to share reminder list see this article https://support.apple.com/en-in/guide/iphone/iph2a8f9121e/ios
When you share a list from iPhone to Mac , a mail will be received in Mac IMAP account and a notification on top right corner will appear , you have to click on Join reminder list , now in your Mac enter with the apple id and password used in Mac ( note : the Apple ID and password in iPhone and Mac are totally different ) at www.icloud.com you can view the shared list of reminders created in an iPhone .
See this screen shot of reminder list that was in iPhone is received in www.icloud.com signed in with Apple ID and password on Mac .
And regarding for sharing reminder list from www.icloud.com using a Mac to an iPhone see this article https://support.apple.com/kb/ph12516?locale=en_US
then go In iPhone the invitation is to be accepted by entering in the email account used in iPhone .