I am looking for a way to change the autocomplete field of "Person or Group" to a dropdown list.
I checked the Lookup field solution, that doesn't suit me, i only need to transform the autocomplete to a dropdown list.
To this :
Now click on the newly added drop-down and select "Items" from top dropdown besides formula. Enter the below formula in the formula bar.
Here, top:100 means the top 100 users will be shown. You can check adding different numbers according to your requirement. For the same dropdown, click on properties (right side), we already filled the "Items", now "Value" is to be selected (field of the user to be displayed in the dropdown as options). Select the value you want to show in your dropdown. For your requirement it should be -
This is just a workaround if you have access to PowerApps in your subscription.
OOTB doesn't have that feature. To have a dropdown, try to customize the form using PowerApps.
That is no OOB settings to control the behavior for that column. You can customize it in a InfoPath/PowerApps forms