Is it Important to Learn Design Patterns?
Learning about specific design patterns is analogous to learning about specific data structures. All else being equal, it's better to have learned them than not to have learned them, but it's okay if you can't remember the details of the more obscure ones. However, you should be able to find references (e.g., via Google) to look up the details as needed.
There's basically one cynical reason and two "normal" reasons to learn design patterns.
The cynical reason is that sometimes someone might ask you about design patterns during a job interview, and it'll "look bad" if you don't know them. It's one of those silly, unfortunate realities about job interviewing. It's like how you want to know how to dress appropriately: even if it doesn't correlate very much with your software development skills, dressing inappropriately will probably hurt your chances of getting hired.
The other two reasons are (1) it acts as a shared language that you can use to communicate with other developers, and (2) it's a tool you can use to solve some of the problems you might encounter during software development.
Going back to the analogy with data structures, you'll sometimes be discussing how to solve a problem with a fellow developer, and they might say something like, "We can use a hashtable for that". If you know what a hashtable is, this sentence communicates a lot of information about the design your partner has in mind. On the other hand, if you don't know what a hashtable is, it's not a super big deal: they can explain it to you. However, their explaining it to you is a form of investment, where they're spending time upfront teaching you the meaning of the term because of their belief that that data structure will be useful again in the future, and it's worth having a label we can use to refer to this commonly occurring data structure. This is the shared language being developed.
It's the same thing with design patterns. Working together with your colleague, they might propose, "Let's use the decorator pattern here", and if you have that shared language, that can communicate a lot of information very succinctly.
When working alone, sometimes you'll encounter a problem where a particular data structure makes solving the problem much more straightforward. Similarly, sometimes there's a design pattern that might solve specific problems very easily. If you don't know the correct data structure/design pattern, that doesn't mean it'll be impossible to solve the problem. It just means you're going to be spending some brain power rediscovering and reinventing things that other people have already figured out and documented.
So learning about different design patterns is about as important as learning about different data structures. Ideally, you learn them organically by applying them to the real-world problems you encounter, instead of just buying a big book full of them and memorizing them one after another. However, it's difficult to see opportunities to apply patterns/structures if you're unaware of them, so it's worth perusing through these big books of patterns/structures so that you can see what's available out there.