Ansible regular expression to match a string from a list of line

I'm trying to read a content of file from remote file. but i want the message to be displayed only matched UUID from fstab file. but when i ran below playbook it is throwing below error.

playbook:

- name: read content from a file
  hosts: all
  become: true
  tasks:
    - name: read a content
      slurp:
        src: /etc/fstab
      register: output
    - name: print
      debug:
       msg: "{{ (output['content'] | b64decode).split('\n') | regex_search('^\\S+/UUID\b.*', multiline=True) }}"

error:

TASK [print] *************************************************************************************************************
FAILED! => {"msg": "Unexpected templating type error occurred on ({{ (output['content'] | b64decode).split('\n') | regex_search('^\\\\S+/UUID\b.*', multiline=True) }}): expected string or bytes-like object"}

First, when I run your playbook I don't get an error; I just get no output from the debug task:

"msg": ""

If you're looking for a list of lines that start with UUID, you could do this:

- name: read content from a file
  hosts: localhost
  tasks:
    - name: read a content
      slurp:
        src: /etc/fstab
      register: output
    - name: print
      debug:
       msg: >
         {{
           (output['content'] | b64decode).splitlines() |
           select("match", "UUID")
         }}

On my system, this produces:

ok: [localhost] => {
    "msg": [
        "UUID=2fbad834-42b2-48fd-868d-3eea12e144de /                       btrfs   subvol=root00,compress=zstd:1 0 0",
        "UUID=c72e509c-453a-4e62-8cea-23ad112765d3 /boot                   ext4    defaults        1 2",
        "UUID=F3B3-4F58          /boot/efi               vfat    umask=0077,shortname=winnt 0 2",
        "UUID=2fbad834-42b2-48fd-868d-3eea12e144de /home                   btrfs   subvol=home00,compress=zstd:1 0 0",
    ]
}

If you wanted a line matching a specific uuid, you could do this:

- name: read content from a file
  hosts: localhost
  tasks:
    - name: read a content
      slurp:
        src: /etc/fstab
      register: output
    - name: print
      debug:
       msg: >
         {{
           (output['content'] | b64decode).splitlines() |
           select("match", "UUID=c72e509c-453a-4e62-8cea-23ad112765d3") |
           first
         }}

On my system this produces:

ok: [localhost] => {
    "msg": "UUID=c72e509c-453a-4e62-8cea-23ad112765d3 /boot                   ext4    defaults        1 2\n"
}