I'm glad to hear you solve the problem ,if you have any issue about SharePoint, you are welcome to raise a ticket in this forum.
By the way, since the Microsoft Q&A community has a policy that "The question author cannot accept their own answer. They can only accept answers by others.". and according to the scenario introduced here: Answering your own questions on Microsoft Q&A, I would make a brief summary of this thread:
[Sharepoint List New Item Showing as classic instead 'online'/ new view]
Issue Symptom:
We have a sharepoint list, in Sharepoint Online.
When use the specific 'new item' link, to share for users to raise items for the list, it keeps viewing in 'classic' not sharepoint online version.
It never used to do this, and cannot work out what setting is triggering this.
We have gone into the advanced list settings and set the experience as 'New' but it still keeps defaulting to classic.
When on the list and click 'new item' it shows in the new experience, but only when you use the stand alone link for adding new it defaults to classic.
Any ideas what setting might be triggering this and how to turn this off?
Current status:
We ended up having to go to microsoft, but putting the solve out here incase anyone else needs it.
It was because we had a column for 'ratings' and 'number of likes'. So if you are using likes or ratings, this will cause it to trigger classic mode.
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