Well, hold your horses, is what I would say. The use of logger is deprecated, but that does not mean that the entire widget will get deprecated. Albeit, development on the Customstring, looking at the Github repo, seem dead.
But it is only deprecated in Mx11. So it is likely still a couple of years before your upgrade is due. Time you have to refactor the widget and come up with an alternative widget written in react. Make sure you give it the same name, make it have the same parameters, same return, and internally make the widget have your own brand new code.
Once you have the new widget, overwrite the current one in the /widget and in Studio Pro trigger ‘update all widgets’.
A bonus is that creating the new widget-version is far more fun compared to replacing a deprecated widget by a less functional one.
Extra tip: Team up with others, like Nour, help each other out.
Extra tip 2: Fork the Github project. Or better: ask the project members to invite you and build on their reputation. Make Customstring Mx10.
Good luck, hope you get this done.
If you need to remove the custom string from the project and the format string does not provide you the needed result of your data logic, maybe create a non-persistable entity and create the attributes that you need to show on your page as string custom logic and add your values, you can either create it before landing on the page or by using a data view with microflow data source to create the custom non-persistable view.
Thanks Nour for the suggestion. Replacement means a project of several months in this case – that simply is not an option...