Blender not responding while running my script When running my script, it can take up to a few hours depending on how detailed my object is.

While blender is running my script, blender changes its status "no response" (not sure if it's the correct translated word, since I only know the german term for it which is "Keine Rückmeldung") meaning I cannot do or click anything on blender while it's running.

So my question is, is there a way to have a remaining-process-time-ish-pop-up or just a script-is-running-do-not-turn-off-blender-pop-up?
Short answer: No
See: Strange errors using ‘threading’ module

Python scripts run 'blocking', Blender will wait until finsihed. It isn't thread-safe to run python in parallel. You may be able to get around the issues with Blender crashing with python running own threads using a modal operator with timer: Blender UI Multithreading Progressbar. Also consider if a modal operator running the background is suitable for your use case (let it return {'PASS_THROUGH'}).

If your scripts run for hours, you should also investigate why they are so slow. See here what hurts performance: Python performance with Blender operators