Each custom field type has its own limits and the custom field limits are per entity. For example, In the Growth plan, you can add 150 contact fields, 150 account fields, 150 deal fields and 150 custom module fields respectively.
Custom field limit per plan
What happens to the extra fields on the downgrade?
When you downgrade your plan, so does your maximum field limit.
Say, for instance, you have downgraded from Enterprise to Pro.
As a Pro user, you could add up to 250 custom fields.
You have added 300 fields in total.
Now that you have opted for the Pro plan, your limit is 250. So, there are 50 extra fields.
" The extra fields need to be deleted"
* Please delete the extra fields before you downgrade.