A faster solution - use plpgsql

1 - the original function

CREATE OR REPLACE FUNCTION port_conflicts4(bigint, text) RETURNS SETOF ports_conflicts_matches AS $$
  SELECT DISTINCT PC.id, CLP.port_id
    FROM commit_log_ports CLP JOIN ports_conflicts PC 
                              ON (PC.id = $1 AND CLP.port_name_revision ~ $2);
$$ LANGUAGE SQL STRICT;

2 - the plpgsql function

CREATE OR REPLACE FUNCTION port_conflicts5(bigint, text) RETURNS SETOF ports_conflicts_matches AS $$
  DECLARE
    a_ports_conflicts_id ALIAS FOR $1;
    a_regex              ALIAS FOR $2;

    l_regex text;
    r       ports_conflicts_matches%rowtype;
  BEGIN
    l_regex := '^(' || a_regex || ')';
    
    FOR r in SELECT distinct a_ports_conflicts_id, port_id FROM commit_log_ports WHERE port_name_revision ~ l_regex
    LOOP
      RETURN NEXT r;
    END LOOP;
  END;

$$ LANGUAGE 'plpgsql' STABLE;

3 - the query

freshports.dev=# explain analyse SELECT PC4.*                                                                                
  FROM ports_conflicts PC, LATERAL (SELECT * FROM port_conflicts5(PC.id, '^' || PC.item_value || '$')) PC4;
                                                        QUERY PLAN                                                        
--------------------------------------------------------------------------------------------------------------------------
 Nested Loop  (cost=0.26..20420.46 rows=1020000 width=12) (actual time=0.507..11.971 rows=60 loops=1)
   ->  Seq Scan on ports_conflicts pc  (cost=0.00..20.20 rows=1020 width=40) (actual time=0.008..0.010 rows=5 loops=1)
   ->  Function Scan on port_conflicts5  (cost=0.26..10.26 rows=1000 width=12) (actual time=2.388..2.389 rows=12 loops=5)
 Planning time: 0.066 ms
 Execution time: 11.998 ms
(5 rows)

freshports.dev=# SELECT PC4.*                                                                                
  FROM ports_conflicts PC, LATERAL (SELECT * FROM port_conflicts5(PC.id, '^' || PC.item_value || '$')) PC4;
 conflicts_id | port_id 
--------------+---------
           21 |   41490
           21 |   44391
           22 |   16965
           22 |   26125
           22 |   32408
           22 |   37760
           22 |   39843
           22 |   40654
           22 |   41123
           22 |   41266
           22 |   42249
           22 |   42846
           22 |   42892
           22 |   44547
           22 |   45081
           22 |   45399
           22 |   45987
           22 |   46004
           22 |   46302
           22 |   46670
           22 |   46837
           22 |   48249
           22 |   48566
           22 |   48568
           22 |   48611
           22 |   49699
           22 |   49702
           22 |   49704
           23 |   38042
           23 |   44644
           23 |   40421
           23 |   48630
           23 |   39708
           23 |   40520
           23 |   48881
           23 |   46760
           23 |   49666
           23 |   35631
           23 |   44827
           23 |   42376
           23 |   45526
           23 |   49671
           23 |   42255
           23 |   46955
           24 |   46502
           24 |   44539
           24 |   47245
           24 |   44540
           24 |   31147
           24 |   42259
           24 |   40750
           24 |   32558
           25 |   46699
           25 |   32193
           25 |   40409
           25 |   28808
           25 |   49668
           25 |   45440
           25 |   48244
           25 |   42383
(60 rows)

freshports.dev=#