Sure:
I have a list of worksites. Column names are like:
Name;Latitude;Longitude;Elevation;Hazards;Last Inspected;
1 - Select flow 'Copy Shareporint List items into a CSV each week'
2 - Opt to use my SharePoint Account
3 - 'Get Items'
3.1 Select my Sharepoint Site
3.2 Select my List Name
4 - 'Create CSV Table'

5 - 'Get Current Time' unchanged from default option utcnow();
6 - 'Create File'
6.1 Select a subdirector in my 'Onedrive for Business' account
7 - Select Save Flow
8 - Run Flow
8.1 - Flow takes approximately 2 seconds to run
8.2 - Out out is the whole list in CSV format, looks like I would expect (some information blurred in screenshot)

Now - I want to customise this to only output a few columns.... Back into 'Edit Flow'
9 - Select 'Columns' to 'Custom'
9.1 - Use the dynamic selector to add column names to the required header columns, in this case I have selected Name, Laititude and Longitude

My expectation is that this would result in a CSV file with:
Headers in the columns
The Headers called 'Name', 'Latitude', and 'Longitude'
The date in those columns corresponding to the list columns 'Short Name', 'Latitude' and 'Longitude'
10 - Save the flow
11 - Run the flow
11.1 - Flow takes 40 seconds (flow using 'default' attributes took 2)
12 View CSV file:
CSV File is all on one line. Data is not consitend (some list content is concatenated), lots of ascii control characters (\r\n)
Basically, a mess.

I'm happy to send the full output file to the Microsoft team for a look, but I won't paste it to a public forum.
Hope that helps.
Dan