I have 25 categories for my posts. I want to add custom fields to only 5 of them. The other 20 do not need them. How can I achieve this?? I'm using Metabox AIO and can add the custom fields via settings - taxonomy - category but don't see how to select specific categories.
You can use the Advanced Location Rules (MB Include Exclude), however it supports loading a field group for a specific post based on the condition as in the documentation https://docs.metabox.io/extensions/meta-box-include-exclude/
not for a specific term as you mention. I will inform the development team to consider supporting this feature in future updates.