Using List Button and Flow URL, we can invoke the Flow from related list Button in Salesforce Lightning Experience. Please check the following with the Steps.
1. Create a Flow.
2. Get the Flow URL.
3. Create a List Button with URL and use the Flow URL.
4. Add the List Button to the related list in the Parent object page layout.

Output:

can we pass parameter/attribute to flow from the related list?
And can the flow is not rendering properly. Any way to define that.
Yes. Check this – https://help.salesforce.com/articleView?id=flow_distribute_internal_url_variable.htm&type=5
can we call LC/LWC from list button.
No. Vote for this idea – https://trailblazer.salesforce.com/ideaView?id=0873A0000003TXFQA2
this is not working in lightning Community. is there any other additional step which we need to perform?
Are you getting any error?
How do you selected record Ids to flow?
You can pass values from the current record – https://help.salesforce.com/articleView?id=sf.flow_distribute_internal_url_variable.htm&type=5
how did you add a custom button to a related list? I only see options to add standard buttons?
Create a List Button with URL and use the Flow URL. Add it to the Page Layout.
You also have to make sure you add the new button in Search Layouts. Go to the Object Manager for the related list object > Search Layouts > Under Custom Buttons move your button from available buttons to selected buttons.
Any way to get the flow in a pop up window instead of taking up a full page in same or new tab?
I think no. May be in the future, if LWC is supported, it can be done.