sharePoint Lookup field which referecne a list that contain 2 million records is not working

[johnjohn123]

I have a Parent SharePoint online list which contain over 2 million records:-

and inside another list (Child list) i have a lookup field which reference the above parent list, as follow:-

and inside the Parent list i added the Title as an index column, as follow:-

now when i customized the Child list's Create/Edit form using Power App, i will get these warning + the lookup field on runtime will be disabled:-

Any advice ? per my knowledge that defining the correct Index on the Parent list should allow us to reference the list using Lookup field, even if the list has more than 5,000 records... but seems this is not working in my case? am i missing something?

Thanks

[johnjohn123]

I have a Parent SharePoint online list which contain over 2 million records:-

and inside another list (Child list) i have a lookup field which reference the above parent list, as follow:-

and inside the Parent list i added the Title as an index column, as follow:-

now when i customized the Child list's Create/Edit form using Power App, i will get these warning + the lookup field on runtime will be disabled:-

Any advice ? per my knowledge that defining the correct Index on the Parent list should allow us to reference the list using Lookup field, even if the list has more than 5,000 records... but seems this is not working in my case? am i missing something?

Thanks