Hi @Heather_Johnson2 , @lpb , this is actually possible! Perhaps it is a recent feature that was ‘quietly’ released.
The key is for the custom fields to be added to the org’s library. Once a task with custom fields is converted to a project, the fields data will be added to the project’s fields, which you can see in the project actions dropdown > Edit project details.
To have these same fields show up in the Portfolio that the project is added to, simply add the same custom fields to the portfolio from your field library so that the same values will show up in your portfolio, as they did in the project that the original task belonged to.
This actually comes in handy in the early stages of a project, before it is actually considered an ‘official’ project. For example, when an asset is simply a task in a ‘Potential Purchases’ project; once the asset has been reviewed and the team decides to proceed with a purchase, then they can use a rule as an action dropdown (eg. ‘For purchase’) that converts the task into a project, based on a template (with all the required steps for the purchase), whilst adding it to a portfolio ‘Real Estate Properties’.
The project ‘Potential Purchases’ and the portfolio ‘Real Estate Properties’ share the same fields (such as footprint area, address, property type, landlord name etc), so these values will be transferred from the original task (in ‘Potential Purchases’ project) to the new project (in ‘Real Estate Properties’ portfolio).
The ‘Learn more’ links takes you to the guide article here, which is unfortunately lacking the above information regarding custom fields being mapped.