This Solve:

CREATE SEQUENCE ir_attachment_id_seq START 1;

then 

SELECT setval('ir_attachment_id_seq', (SELECT MAX(id) FROM ir_attachment));

I had a similar issue on a custom table that I had changed the name of.

The fix was to recreate the sequence in the database (through pgadmin or other database management tool)

My table was called 'sale_partexchange' so you can just replace the table name with your one and run the following SQL statement.

DROP SEQUENCE IF EXISTS sale_partexchange_id_seq;
CREATE SEQUENCE sale_partexchange_id_seq START WITH 1 INCREMENT BY 1 NO MINVALUE NO MAXVALUE CACHE 1;

im having a pretty weird problem as well, when i try to go into "Technical -> sequencing" in order to change the sequence number of my invoices, i get inmediatly a server error, where it says

Traceback (most recent call last):
  File "/odoo/odoo-server/odoo/api.py", line 1039, in get
    value = self._data[key][field][record._ids[0]]
KeyError: 254

so i cannot change the invoice sequences, at the same time, checking the history of invoices, the sequence never changed the year from 2021, it stuck, right now begginning 2023, we have inv/2021/0001

This will do the job. Run in PGADMIN or commandline
remove -- to execute

DO $$
DECLARE
_record RECORD;
_max BIGINT;
_exec VARCHAR;

BEGIN

FOR _record IN
(
SELECT table_schema,
*
FROM information_schema.COLUMNS
WHERE column_name = 'id' and table_name != 'xxx')
LOOP
execute format('select max(id) from %s', _record.table_name) into _max;

IF _max is NULL THEN
_max = 1;
ELSE
_max = _max + 10;
END IF;

_exec = 'CREATE SEQUENCE IF NOT EXISTS ' || _record.table_name || '_id_seq START ' || _max;
RAISE INFO '%', _exec;

execute _exec;



END LOOP;
END;
$$ ;