HI Punit, As per salesforce documentation- https://developer.salesforce.com/docs/component-library/documentation/en/lwc/lwc.create_components_focus ,
"Only 0 and -1 tabindex values are supported. Assigning tabindex="0" means that the element focuses in standard sequential keyboard navigation. Assigning it tabindex="-1" removes the element from sequential keyboard navigation"
As per salesforce documentation- https://developer.salesforce.com/docs/component-library/documentation/en/lwc/lwc.create_components_focus ,
"Only 0 and -1 tabindex values are supported. Assigning tabindex="0" means that the element focuses in standard sequential keyboard navigation.
Assigning it tabindex="-1" removes the element from sequential keyboard navigation"
Related: https://webaim.org/techniques/keyboard/tabindex
Hope this helps you. Please mark this answer as best so that others facing the same issue will find this information useful. Thank you