@Muhammad MuslimI'm glad that you were able to resolve your issue and thank you for posting your solution so that others experiencing the same thing can easily reference this! I have summarized and posted the solution here for you in case you'd like to "Accept " the answer.
Issue: Decommissioned AVD Classic keeps showing up on RD App Subscription
Solution: Please make sure that after removing all classic objects, you also delete the classic tenant. https://learn.microsoft.com/en-us/powershell/module/windowsvirtualdesktop/remove-rdstenant
Customer shared that - "Thank you for your response, Karishma. After checking once more I realized the subscription number, I pulled from Get-RdsTenant did not match the current subscription my client had. This meant I was looking at the wrong subscription the entire time. This issue is now resolved"
Accepted answers show up at the top, resulting in improved discoverability for others.