I'd never worked on a large MVC project before that had a front-end, back-end, data bases, 25 different view files, both C# and JS, etc.
I get assigned simple bug fix tickets but spend 1/2 to 3/4 of the day trying to figure out how all these files interact with each other. Its difficult for me to decipher a lot of the code. I'm not sure which code to touch and which code is a different department's responsibility.
I have been in a similar situation picking up my first full time job as a junior software dev after doing internships, so I can somewhat understand the overwhelmed feeling that you are feeling now. I had done work on very large systems in my internships as well, but mostly on small, specific parts of it. At my first full time job, however, most of the work was done as a full stack developer, and on very complex projects.
What had helped me the most was a wonderful mentor, who helped guide me through the structure of the project on a high level. Even then, it took me quite a lot of time to understand the project itself. For several sprints, I was a week or two behind schedule, but I began to piece things together little by little. It took me around a month or two before I understood all the pieces of the project. Throughout, by communicating with my team about my progress in daily scrums, and keeping them updated, my team was always supportive, and understood that it would take time to learn everything.
Something else that helped was the linear structure of my stories; I worked through the entire stack story by story to achieve my goal, and by the end of it, I had a good understanding of the entire stack, matching the top-down explanations given by my mentor.
I then moved onto a different team in the same company, for a different project, and was able to once again pick up the structure. This time, I was forced to be more independent, due to the time crunch and the members being busy on their own. There was no mentor, but I made use of confluence and the wiki to figure out parts of the structure, asked the other team members when I got blocked for more than half a day, with the results of my research from confluence, the wiki, and the web, and eventually mapped out the workings of the second project.
I did post a lot of info, but I believe that yes, being overwhelmed for a new job is very normal. It took me about a month to thoroughly understand the projects I worked on (although this is not particularly fast, it is still acceptable in most companies), but none of my team members have derided me about it.
My advice, from my experience, is to be straightforward and communicate to your team. Tell them about your confusion about how parts fit together. Do update them every now and then on your progress, perhaps they can offer tricks to unblock you. In terms of how often to ask questions, and how to ask questions, this resource about the method to ask is helpful, although you may already know the general gist.
Most of all, as a full time job working with a large codebase, actively listen and ask questions about things you don't understand. If you have work updates, you can figure out who does what, so you know who to ask. Internships are different in that we are not expected to understand the whole picture, given the short duration, but at a full time job, understanding the high-level overview of a project is very useful. You may also be working with your team for a long time, so knowing what they do and what they can help you with is very useful.
Confidence in your job is built up steadily, it is perfectly fine to take it slow and build up your understanding over time.
I hope some of my own experiences starting out can help a little, and I wish you the best of luck! Know that starting off your full time career is definitely not easy, especially in times like this, but you can pull through with some good communication and persistence.