Yes, I brute forced with Icelandic (before LingQ existed) and eventually got to C1 level after a few years. I had the same issue as you, there was almost no content whatsoever I could even practice or learn with – of course there is much more out there nowadays. So at the time, a lot of what I learned from was like 1920s newspaper articles I found for free online on archive sites. I also found a few recipes and knitting patterns I struggled to learn with. I learned using a method almost exactly the same as what LingQ uses.
It IS possible. But it takes a lot of time and is very frustrating, as you have found out.
Since your partner speaks it, I would see if they can even write some texts for you, or help you order something. Children’s books and materials for foreigners aren’t necessarily easier than standard materials meant for adults. In fact the former types of materials can even be harder to understand because they use less words and contain less context clues for the rest of the sentence.
The other method someone mentioned here also works well. If there is another dialect or language similar enough, but which is easier to understand or has more practice materials, learn that first and then switch back to the other dialect. For example I found that Faroese and Scandinavian were both easier for me to learn than Icelandic, so I switched to those for a bit and when I eventually returned to Icelandic I found my comprehension was much better.
Now I’m learning Ukrainian which is hard to find decent resources for despite being a huge language. So I have gotten chatgpt to write or rewrite texts for me, and have found children’s books for free to read online and I copy the words into LingQ, stuff like that. I also try to read about subjects I’m already familiar with which are using loanwords from English, such as computing or American news events.