If the issue persists every time you launch, follow these deeper troubleshooting steps:
Click the Workshop button in the game launcher (rather than "Play") and manually accept the Workshop ToS if prompted. Long-Term Solutions for Permanent Fixes aoe2 validating subscriptions
Here is a comprehensive guide to understanding and fixing this issue. If the issue persists every time you launch,
Press Ctrl + C to skip the validation screen and enter the main menu. Some players also report success by spamming the spacebar or hitting Enter . aoe2 validating subscriptions