Hi @Juhi Saxena - Thanks for reaching out & posting on the MS Q&A!
I see the same thing but Function Apps running on custom containers are not supported for Portal Development and it's possible that those are just the default options during creation only. I will raise this internally for further clarity & update this answer. In the meantime, please go ahead and create your Functions App with the existing options in the dropdowns. After the creation is completed, you can navigate Deployment Center -> Settings to get the additional options populated in dropdowns:
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