If you’re on the beta, under Taskbar settings > Taskbar behaviors, you can now select options under Show smaller taskbar ...

But a new feature might fix that by automatically making taskbar icons smaller as necessary. The Windows Insider blog details the new feature on the latest Beta and Dev versions of the Windows 11 ...

Microsoft is testing a new taskbar icon scaling feature that automatically scales down Windows taskbar icons to show more apps when it gets too overcrowded. The feature is gradually rolling out ...