Aggregating relationships use two sums and calculate the percentage.

Tables\Columns\TextColumn::make('leads_sum_connected')
        ->sum('leads', 'connected')
        ->label('Connected'),

    Tables\Columns\TextColumn::make('leads_sum_connection_request')
        ->sum('leads', 'connection_request')
        ->label('Connect Req'),

  leads_sum_connected / leads_sum_connection_reques 

Tables\Columns\TextColumn::make('connected_percent')
        ->label('Connected %'),