@Miki
If you know which directory to search you can include that is part of the prefix folder1/subfolder2/. Unfortunately you cannot search all folders in the portal or in Storage Explorer nor do wild card searches work. Blob service only supports filtering by blob prefix and not by suffix. Someone has already opened an existing feedback item for this, feel free to comment and follow for any updates.
One method which might work for you is listing all the blobs in PowerShell with Get-AzStorageBlob and use that to do a wildcard search for the file. See the below example:
Get-AzStorageBlob -Context $ctx -Container $containerName | Where-Object {$_.Name -like "*filename*"}
Hope this helps! Let me know if you have further questions or issues and I will be happy to assist.
-------------------------------
Please don’t forget to "Accept the answer" and “up-vote” wherever the information provided helps you, this can be beneficial to other community members.