I’d wager the root CA certificates on the device are expired since it hasn’t been updated in ages. So it can’t trust certs signed with the new root CAs.

Some I’ve tried/heard of (sorted by amount I’ve used them):

• Language Transfer (Audio-based course in the format of a teacher-student conversation with explanation of concepts etc. Completely free but takes donations)
• Clozemaster (Mostly fill in the right missing word, small challenges format)
• Memrise (Memorizing common phrases, spoken by a cast of real people with distinct dialects etc.)
• Mango (More feature-rich, similar to Duolingo but better IMO. Many libraries offer this, worth looking into)
• Babbel (Barely touched this one but think it’s similar to Duo)
• Lingonaut (New thing, don’t think it’s live yet but I think it’s focused around community-driven features that Duolingo cut out to replace with AI)

It’s coming along better than before. I’d mostly attribute it to immersion training with podcasts, books, and video games in my target language. I am horrendous when it comes to sitting down and taking the time to study deliberately, but I do learn quite a bit from procrastinating in my target language.