Italki isn’t useless at all. It’s just not the best tool to look for language exchange partners. There aren’t many Germans looking for language exchange here but when you scroll through the German forum you’ll find many language partner requests by fellow German learners, so that could be a start to practice with them. You can also take part in German discussions in the forum, ask questions about German and post German notebook entries. There are Germans who answer a lot of questions and correct notebook entries, so you’ll receive lots of free help.
Italki has bought an app called Lingbe, which can connect you instantly with language exchange partners all over the world. You can set German as your target language and by just pushing the call button you’ll get connected to German speakers.
Here on italki, it helps to write something about yourself in your profile, so potential partners can see if you’re a good fit and you could correct Portuguese notebook entries and answer questions about Portuguese. If you help other people, you’re also more likely to receive help.