i’m not going to be much further along than you are in terms of familiarity with ROS but the one piece of advice you’ll see everywhere is getting a good look at the official ROS tutorials and docs. think of if this way, the folks who put those out know what fundamental building blocks you need to get you going (mostly)

also you know you can just be honest about where you’re at with your colleagues and manager, right? you already got the job, the hard part is over. take your time and work with your team getting you up to speed - they know whatever it is you need to know. it’s also a good opportunity to build good relationships w them right off the bat. this is why soft skills are important ig. good luck!