Is it possible to create an index in PostgreSQL for a field that does not require unique values?

Yes, in PostgreSQL, you can create an index for a field whose values are not unique. Indexes are used to speed up data search and sorting, and they do not necessarily require unique values. For example, you can create a regular B-tree index on a field where values are repeated:

CREATE INDEX idx_field_name ON table_name(field_name);

Such an index will help accelerate queries with filtering on this field, even if the values are repeated.