Hi Sumaira,
You would like to create a field for Lead and this field shows the latest Task of the Lead, and the field also display as a column on the view, right?
If so, we can create a Task lookup field for Lead, and create a workflow to automatically update this lookup field when a Task regarding Lead is created, then create a flow to manually update all Lead based on existing Tasks.
Step 1. Create a Task lookup field for Lead.

Step 2. Create a workflow. Activate.



Step 3. Create an instant cloud flow.



Run it, if it runs successfully, turn off it or delete it.