I've been working as a developer for a while now but I work a lot on small bugs or on established products - how should I go about learning larger designs and design patterns? I feel like my knowledge is lacking in this area.
I recommend you to buy some proper books to get familiar with well written design patterns. Classics are "Design Patterns" from the Gang of Four (GoF), "Pattern-Oriented Software Architecture" by Buschmann et al. or "Enterprise Integration Patterns" by Hophe and Woolf which patterns are partly available on the website https://www.enterpriseintegrationpatterns.com/.
The first two books I consider almost a must read. Actually it's not about reading them but learning the patterns. More about this here: https://www.industriallogic.com/papers/learning.html