I'm not aware of a free Azure subscription to do this. However, I would definitely recommend giving the Microsoft Applied Skills a look which are free to try:
This will show you all available Azure Administrator related Applied Skills.
If you do one of the applied skills from the above link you'll be given a lab VM (free) during the assessment and be asked to complete tasks to validate your skills.
These applied skills are not proctored and if you do not pass you can retake 24 hours later for free (see here for more info :https://learn.microsoft.com/en-us/credentials/support/retake-policy)
Whilst they are an playground labs, they do provide a free way to get real hands-on exposure to test your skills against real tasks that are relevant. I would advise you review the study material before you take the skills to familiarise yourself.
Hope this helps, if it has, please mark as accepted.
Dan