A way to optimize sql about the last temporary-related row

Hello everyone,
Sorry to bother you but I have a query that is driving me crazy.

I need to have the last valid record at a temporal level according to a
specific parameter.

First some data:
Linux Rocky 8.10 environment, minimal installation (on VM KVM with
Fedora 40).
Postgresql 16.3, installed by official Postgresql guide.
effective_cache_size = '1000 MB';
shared_buffers = '500 MB';
work_mem = '16MB';
The changes are deliberately minimal to be able to all to simulate the
problem.

Table script:
CREATE TABLE test_table
(
 pk_id int NOT NULL,
 integer_field_1 int ,
 integer_field_2 int,
 datetime_field_1 timestamp,
 primary key (pk_id)
)

-- insert 4M records
insert into test_table(pk_id) select generate_series(1,4000000,1);

-- now set some random data, distribuited between specific ranges (as in
my production table)
update test_table set
datetime_field_1 = timestamp '2000-01-01 00:00:00' + random() *
(timestamp '2024-05-31 23:59:59' - timestamp '2000-01-01 00:00:00'),
integer_field_1 = floor(random() * (6-1+1) + 1)::int,
integer_field_2 = floor(random() * (200000-1+1) + 1)::int;

-- indexes
CREATE INDEX idx_test_table_integer_field_1 ON test_table(integer_field_1);
CREATE INDEX xtest_table_datetime_field_1 ON test_table(datetime_field_1
desc);
CREATE INDEX idx_test_table_integer_field_2 ON test_table(integer_field_2);

--vacuum

vacuum full test_table;

Now the query:
explain (verbose, buffers, analyze)
with last_table_ids as materialized(
  select xx from (
  select LAST_VALUE(pk_id) over (partition by integer_field_2 order by
datetime_field_1 RANGE BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED
FOLLOWING) xx
  from test_table
  where integer_field_1 = 1
  and datetime_field_1 <= CURRENT_TIMESTAMP
  ) ww group by ww.xx

),
last_row_per_ids as (
  select tt.* from last_table_ids lt
  inner join test_table tt on (tt.pk_id = lt.xx)

)

select * /* or count(*) */ from last_row_per_ids;

This query, on my PC, takes 46 seconds!!!
I was expecting about 2-3 seconds (according with my other queries in
this table) but it seems that the xtest_table_datetime_field_1 index is
not being used.

Do you think there is a way to optimize the query?

Thanks so much for the support,

Agharta