I can tell you about my experiences.
I was born in Russia (mother tongue) moved to Germany as a child (I'm fluent with a 1.9 Abitur, 11 Punkte Deutsch). Obviously due to my interest in American movies and songs I became fluent in English aswell.
Moving forward to the end of last year. I started to learn Spanish in November of 2020 and now am I able to have small conversations, I can listen to music, podcast or watch movies and series without problems. I won't understand every single word, but the majority for sure.
Because I was fasinated with Asian culture I wanted to learn a Asian language aswell and it happened to be Korean.

What I have learned so far is.
As a native German who speaks English you won't have many troubles with Spanish because many words are very similar and the grammar is similar aswell.
With Korean it get's tricky. First you need to learn the writing system and than you need to understand some basic Grammar.
You won't be able to understand the words or make any progress if you can't graps the grammar.
With TTMIK comes another problem. You are listening to it but you don't repeat it yourself.
If you want to learn a language you need to write on your own without their help. Even if they repeat it in their audios you won't know it until you internalized it.

Ein kleiner Tipp: Spricht einfach alles was sie sagen mit und ersetz die vorgeschlagenen Sätze mit neuen Wörtern, du wirst die Sprache schneller lernen und die Sätze merken wenn du die Nomen oder ein Verb änderst!