root@ute:~# mysql 
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 9
Server version: 8.0.33-0ubuntu0.22.04.2 (Ubuntu)

mysql> select c,hex(c),upper(c),hex(upper(c)) from t_utf8mb4_0900_ai_ci;

+------+--------+----------+---------------+
| c    | hex(c) | upper(c) | hex(upper(c)) |
+------+--------+----------+---------------+
| ä    | C3A4   | Ä        | C384          |
| ß    | C39F   | ß        | C39F          |
+------+--------+----------+---------------+

2 rows in set (0,00 sec)

Python 3.10.8 (tags/v3.10.8:aaaf517, Oct 11 2022, 16:50:30) [MSC v.1933 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> 'ß'.upper()
'SS'
>>>

~ # php -v
PHP 7.4.33 (cli) (built: Nov  2 2022 16:00:55) ( ZTS Visual C++ 2017 x64 )
Copyright (c) The PHP Group
Zend Engine v3.4.0, Copyright (c) Zend Technologies

~ # php -a
Interactive shell

php > print mb_strtoupper("äöüß");
ÄÖÜSS
php >                        

14:42:40.572 "ä".toLocaleUpperCase()
14:42:40.592 'Ä'
14:42:47.739 "ß".toLocaleUpperCase()
14:42:47.757 'SS'

Perl 5.32 # perl -MEncode -E "say Encode::encode_utf8(uc qq/äöüß/)";
ÄÖÜSS 

Perl 5.12 # perl -MEncode -E "say Encode::encode_utf8(uc qq/äöüß/)";
ÄÖÜSS