The information you provided are very confused , and your website structures are complicated.
Here are what I found:
1) The problem page URL is a single "Preventivo" post,
2) You are using Toolset form to edit single "Preventivo" post
3) The data source is in another post type "Accommodations", which is using one-to-many relationship with "Preventivo" post type.
4) The custom field "room-internal-name" is in a field group of "Camere" of post type "Accommodations".
So in this case, it needs another post view, to query "Camere" posts, and display field "room-internal-name", output as JSON format.
I have done below modifications in your website:
1) Create a post view "list child Camere post Room Name as JSON format"
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- query "Camere" posts,
- filter by: Select items from the Camere group that are a related to the current post in the loop.
- Enable option "Disable the wrapping DIV around the View"
In view's loop, output JSON data, like this:
...
<wpv-loop>
[wpv-item index=1]{"value":"[types field='room-internal-name'][/types]","label":"[types field='room-internal-name'][/types]"}
[wpv-item index=other],{"value":"[types field='room-internal-name'][/types]","label":"[types field='room-internal-name'][/types]"}
</wpv-loop>
...
Same as your previous post, output the first item without comma.
Here is a document about "Displaying Repeatable Field Groups"
https://toolset.com/documentation/getting-started-with-toolset/creating-and-displaying-repeatable-field-groups/#displaying-repeatable-field-groups
2) Edit the content template "room-quote":
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display above post view:
[wpv-view name="list-child-camere-post-room-name-as-json-format"]
3) Edit the post form "Edit Quote":
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Change the generic field shortcode to:
"options":[[wpv-post-body view_template="room-quote" item="@preventivo-struttura.parent" suppress_filters="true"]]
For the attribute item="@preventivo-struttura.parent", please check this document:
https://toolset.com/documentation/post-relationships/how-to-display-related-posts-with-toolset/#displaying-one-related-item-parent
Please check if it is what you want.