Do any alternatives take a more "fully immersive" approach?
I tried this LibreLingo, but the first question I got was "Which of these is The Sun?".
Once you learn/memorize a few basic Spanish phrases such as "¿Qué significa?" you can stay immersed in the language. When you see a photo of the sun, you need to jump straight to El Sol, not Photo->"The Sun"->"El Sol".
Try Spanish in Latudio [0]. It is not quite for beginners, you need to have at least basic vocabulary, but regarding immersion, it should fit what you are looking for. It uses a listening-first approach and contextual translations with vocabulary and lets you explore words you didn't get in other contexts.
Do they have a version that's not a mobile app? Or will it at least work on the desktop/web browser? I'm not going to use something like that on my phone.
I built https://nuenki.app, which follows a fully immersive approach by immersing you while you browse the web. It translates entire sentences at your knowledge level into the target language, and you hover for definitions/the original sentence/etc.
Once you learn/memorize a few basic Spanish phrases such as "¿Qué significa?" you can stay immersed in the language. When you see a photo of the sun, you need to jump straight to El Sol, not Photo->"The Sun"->"El Sol".