Your experience resonates with me. I also struggled with sheet music later in life, feeling like it was a foreign language I couldn't quite grasp. But hey, you're never too old to learn something new, right?
I found that supplementing my learning with online resources like https://www.artmaster.com really helped. They offer intuitive tutorials that break down music theory in a way that just clicked for me. It's like having a patient teacher right in your living room.
It took time and patience, but eventually, I started seeing progress. Don't be too hard on yourself. Keep at it, and who knows, maybe this new singing club will be just the right environment to challenge yourself and grow as a musician.