Applied Skills assessments have been unavailable for about a week at this point, I'm also trying to take them right now.
There's some information from MS in thispost:
"3/22/24 12:53pm (PST): Due to technical issues discovered during system maintenance, Applied Skills assessment labs are temporarily unavailable. We are working to resolve this issue as quickly as possible and will update this alert message with updated information as soon as it is available. In the meantime, we apologize for any inconvenience and appreciate your patience as we work toward resolution.
*Microsoft Credentials Team"
Hoping it gets resolved soon so we can take the assessments.