Hi, think of the Portals as a web site with a bunch of built features and easy access to your CDS data, don't think it as a canvas app cause it is not what it is
all the customization you make will require web development skills, in regards your questions:
1. Can I have type to search component in power apps portal, whereby just typing a few letters it should search from the data source
--> what you need to search specifically? there is an OOB feature called global search: https://docs.microsoft.com/en-us/powerapps/maker/portals/configure/search
Microsoft is currently extending this feature to allow custom entities search, for the moment it is limited to a few entities
this wouldn't have the behavior of search while typing a few letters, you would need a custom JS control for that
2. Can I make table column resizable and like CRM can I put a small filter (funnel icon) in each column.
Your CRM view is represented by an Entity List in the Portals, you can set the size of the columns in the entity list configuration: https://docs.microsoft.com/en-us/powerapps/maker/portals/configure/entity-lists#entity-list-configuration
There is no feature to add the funnel filter per column, you can in the entity list add filters which would appear as textboxes on top of the list for the filter
3. Can I make Grid within the grid in PowerApps portal
Would require a good bit of JS/Liquid Template customizations: https://docs.microsoft.com/en-us/powerapps/maker/portals/liquid/render-entity-list-current-page
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