2.6 should be capable of dumping 2.4 databases. Might also be worth a try.
P.S.: After the migration you might want to consider using {ARGON2} scheme because slapd-pw-sha2 is only contrib code while slappw-argon2 is a core module. And {SHA512} scheme is also *very* weak because it does only one round of SHA-512 computation.
Will definitely consider moving to argon2, but would probably come post 2.4>2.6 migration.
What you mean by 2.6 should be capable of dumping 2.4 dbs? As in slapcat my 2.6 and import to 2.4? If so, i can definitely try but would be a basic tree with one user for this potential “bug” issue im encountering.