@ClaudiaFr you can use an automation to handle this + any other tagging ideas you have. Order Automator is the app my team built to solve problems like this. We do free customizations as well so if you can't find a rule in the app for your automation idea you can request it to be made.
We have some customers that use both Shopify Flow and Order Automator in combination because of the limitations of Shopify Flow. In your case it looks like you could use it to tag those orders, but if you find things to be limited an app like ours can solve your problems.