how to remove the app icons to the left of the open tabs?

It sounds to me that you mean pinned websites in the Safari tab bar? Read this support document to see what I mean, and this one on Safari tabs in general.

If it is a pinned tab you can't remove, drag it to the right and you can dismiss the window from that position.

Can you add a screenshot for reference?

You're welcome. Now that you know what it is it can be a useful way to park an open window for a revisit at a later time.

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