The following table:

+----+----+
| h1 | h2 |
+:==:+===:+
| A  | B  |
+----+----+

now converts to: (using -t markdown-simple_tables-pipe_tables-multiline_tables)

+----+----+
| h1 | h2 |
+====+====+
| A  | B  |
+----+----+

With pandoc 3.6.4 and before, the alignments were preserved.