Ansible extract sub-string from a matched element of a List variable

I have a variable, which is a list as below:

"test_list": [
     "some text here",
     "server1",
     "command1 parameter1",
     "path/to/command2 parameter2 server1_202012",
     "some more text",
     "New backup file is server1_202019"
    ]

I am trying to extract the substring server1_202019 which is at the end of the line that starts with New backup file.... There is only one line like this and I've tried below option to get the substring.

- set_fact: 
    test_name: "{{ test_list | select('^New backup file is (.+)$','\\1') }}" 

and the output I've received is:

"test_name": "<generator object _select_or_reject at 0x3fe5b40>" 

I've tried below code also, but failed.

- set_fact: 
    test_name: "{{ test_list | regex_search('^New backup file is (.+)$','\\1') }}" 

The error is:

"msg": "Unexpected templating type error occurred on ({{ test_list | regex_search('^New backup file is (.+)$','\\\\1') }}): ..... expected string or buffer"

Could somebody please suggest how I can get the output as below:

"test_name": "server1_202019"

The ansible version I'm using is 2.9

Thanks

Select the item from the list and then use regex_replace. For example

    - set_fact:
        test_name: "{{ test_list|
                       select('regex', my_regex)|
                       first|
                       regex_replace(my_regex, my_replace) }}"
      vars:
        my_regex: '^New backup file is (.*)$'
        my_replace: '\1'
    - debug:
        var: test_name

give

"test_name": "server1_202019"