(.*) Seems to ignore whats coming after it if ":" is optional.
And the port becomes a part of this:

But how to fix it? A fixed set of commonly used TopLevelDomains is not felxible enough.

Try to match a character class that does not contain ':' (i.e. [^:]):

use strict;
use warnings;

for my $uri( qw(https://www.example.de
                http://www.example.de
                https://example.de
                http://example.de
                www.example.de
                example.de:123
                http://www.example.de:445/can?this=happen&too=1#lalala
                http://www.example.de/can?this=happen&too=1#foo
                http://www.example.de:445
               )
           ) {
   print "in  ($uri):\n";

   my (@spl) = $uri 
             =~  m|(http(?:s?))?
                   (?:(?:://)?
                   (w{0,3})\.{0,1})?
                   ((.*)(?:\.)([^:/]*))   # match if it is not a  ":"
                   (?::(\d{0,10}))?
                  |x;

   print 'out: ', join(', ', map { defined $_ ? $_ : '-' } @spl), "\n\
+n";
}

__DATA__

in  (https://www.example.de):
out: https, www, example.de, example, de, -

in  (http://www.example.de):
out: http, www, example.de, example, de, -

in  (https://example.de):
out: https, , example.de, example, de, -

in  (http://example.de):
out: http, , example.de, example, de, -

in  (www.example.de):
out: -, www, example.de, example, de, -

in  (example.de:123):
out: -, , example.de, example, de, 123

in  (http://www.example.de:445/can?this=happen&too=1#lalala):
out: http, www, example.de, example, de, 445

in  (http://www.example.de/can?this=happen&too=1#foo):
out: http, www, example.de, example, de, -

in  (http://www.example.de:445):
out: http, www, example.de, example, de, 445
[download]

Update: Added '/' to character class and example '#foo'

Ok. The spirit reached me. This fixed it:

((.*)(?:\.)([a-zA-Z]*))(?::(\d{0,10}))?

Edit:
@Perlbotics,
Your "match if not" version is the cleaner one. Merci.