Assuming you can accept sorting numbers first, followed by everything else second, then you could use the following logic:

SELECT val
FROM yourTable
ORDER BY
    CASE WHEN REGEXP_LIKE(val, '^[0-9]') THEN 1 ELSE 2 END,  -- numbers first
    val;                                                     -- then sort by val

I’ve got a simpler solution in my follow up question:
The order is correct if I replace COLLATE XGERMAN_AI with COLLATE GENERIC_M_AI.

Extended examples:
Oracle: https://dbfiddle.uk/TOzViGhK
.NET: https://dotnetfiddle.net/gytC9a

Try this bro:

create table t(val varchar2(100));

insert into t 
  select 'AD4' from dual union all
  select 'aA1' from dual union all
  select 'äB2' from dual union all
  select 'aC3' from dual union all
  select '1' from dual union all
  select '2' from dual union all
  select 'XAA2' from dual union all
  select 'X1A1' from dual;
  commit;
  
SELECT val
FROM t
ORDER BY substr(REGEXP_REPLACE(val, '[[:alpha:]]'),0)

This answer is almost the same the link you post (How to sort numbers before letters with linguistic sorting?).
Using ‘[[:alpha:]]’) in this case wiil consider number first inside