I'm with @David_MA about the trigger should work for anyone who creates an item.
And if You make a cloud flow that triggers when an item is created, and someone else creates and item, You are running the flow. It is your flow. They are not running the flow.
They did something in the SharePoint list that triggered Your flow and it functioned on your behalf. Your cloud flows are like an arm of your account.
I'm not IT security expert, so the below statements might not be 100%, but it's close enough,
The only way this would not work is due to some security or permission settings on the sharepoint site or sharepoint list.
For example, you can set sharepoint list item security so that people can only see the items that they created. Therefore, any flow would not allow you to trigger on something that you couldn't see. If it did allow the flow to trigger; it would be almost like a hack (If I'm not allowed to see other items in a list, but I can trigger a flow on items I didn't create, I basically can get the info I'm not supposed to see.)
So now that security control goes in line with the fact that the Cloud flow is Your cloud flow. If you can't see other people's created items, then Your cloud flow can't trigger for them when they create an item. They would need to have their own Cloud flow.
Instead of everyone making their own flow, you can share the flow to the SharePoint list like you did, which is basically like sharing the Cloud flow with a person. Now it should operate like an arm of the SharePoint list and use the security settings for the groups.
I don't think a flow shared with a SharePoint list can be edited by the other users. It is probably only editable by you, list owners, and admins.
Adding the SharePoint list as an owner was probably the best thing you can do for your flow. I share my flows with SharePoint lists and some Teams so that if I leave work or something, then IT can still get into them and edit or use the flows.
