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Hi TaTa_87,
Thanks for posting in the community.
According to your description, you want to an auto-increment Number column and the value will be automatically added based on different values in a Choice column. If so, you can build a Power Automate flow to meet your requirement. Based on my search, here is a thread where members discussed a similar requirement. Please view the thread and check if the flow helps.
Also, if you have more concerns about building a flow, since we have a specific channel Microsoft Power Automate Community coping with such building flow questions, you can post a new thread there for expert help.
Thanks for your understanding.
George