If you want to make the record clickable:
Enable the option to Allow users to expand (or edit) linked records.
Go to the child form settings (not the parent field) and make all fields read-only.
This function also makes the records “expandable” in the gallery view, allowing users to "learn more". For example, you can make the record (card) preview some high-level information by default. But when the user clicks, it pops up to show full details.