How to reduce query running time

I have table1 which contains around 1mln line of records and table2 around 3mln line of data.

I have received the below-mentioned code from my previous post (link) which is updating the table as expected, but is taking more than an hour to update just 100 lines of records.

do $$ 
declare 
  rec record;
  current_joins text;
  current_result int;
begin
  for rec in select joins from table1 loop
     select rec.joins into current_joins;
     execute format('select count(*) 
                     from (
                        select 1
                        from table2 
                        group by %1$s 
                        having count(*)>=1 
                     ) as some_alias;',
                     current_joins) 
              into current_result;
     update table1 set result=current_result where joins=current_joins;
  end loop;
end $$;

Appreciate if somebody could provide me any alternative code to handle the above requirements.

The feature of the table can be seen from the following link (https://dbfiddle.uk/pP_9mKy3) and the previous post can be seen from the following link