I would recommend being upfront about the first job, just make sure your availabilities are set away from each other and tell the manager you'll still be dedicated to starbucks as you are the other job

I have two jobs. I also work a grocery store but in the deli section. I told my managers in March/April I was going to start at Starbucks because I felt like they didn't care weather I worked there or not (they've always treated me like I wasnt important and it shows)
I gave Starbucks my completely open availability, and the other job gets the rest of my time that they wanna schedule me.
I (thankfully) have picked up Starbucks pretty well and I get 30+ hours a week and people ask me to pick up their shifts at least once a week Even though I do that, I checked on my numbers and Starbucks alone still doesn't have a livable wage for me. Some weeks are better than others but I like being extra careful with my money bc if I slip, I'm all I got.
I live alone and pay my own bills all by myself I'm an adult etc.
My other job, though I hate it, the extra 20- 30 hours I can get there, helps ( because I still get paid more there.)
I've now talked to my managers at the grocery store and told them I'm only gonna work there 2/3 days a week VS me working 7 days a week, almost non stop .
That took a big toll on my physical and mental health. You really have to plan around work to even maintain a sleep schedule or social life. Take a day or 2 outta the week to block out so you don't go crazy if you really wanna try both.
Best of luck to you :)

I have two jobs. I get 25 hours at a law firm and then 35-38 hours from Starbucks. Scheduling is really easy if you're upfront with your SM and show that you're able to balance everything

I also work two jobs. I have been with Starbucks for about a month or so now. I work retail and picked up Starbucks to have a little more income over the summer. I get about 15-20 hours but some weeks can drop to about 12 or 13. I also work a slower store and we don’t get as much traffics as other stores around. Now with starting school I just have been making sure that I set me availabilities straight. I set mornings or Starbucks 7 days a week and changed my availability at my retail job to just F, Sa, and Sun and will pick up shifts there if I can. Just gotta schedule accordingly and make sure you let each job know!

You’re fine. I’ve been doing it for years. 20 hours in the minimum to get insurance with Starbucks. If the manager as a need that works outside your other schedule you’ll be fine. Or they can give you a set schedule and have the grocery work around it.

I have 2 jobs. I currently work at a Hy-Vee (grocery store) Starbucks kiosk. I also am a server part time at a restaurant. I can't vouch for a corporate Starbucks, but my manager and assistant manager are wonderful about working with me on my dueling schedules. As long as you work hard to get your availability in a reasonable place (for example I make the most money serving on the weekends and can pick up a shit ton of hours opening 3-4 times a week and working 5 or 9 hour shifts so I have my availability set up to reflect that) you should be fine. My advice is to just keep open communication between you and your managers at each job. It's okay to humanize yourself! People are generally more understanding than I expect them to be. For instance, it was hard at first for me to admit to my manager that I have 2 jobs just because I'm struggling to pay rent and buy groceries, but after I sat down and talked to both my managers about it they were very kind and understanding and I felt like they almost respected me more for it. Sorry for the ramble, I just love giving my 2 cents on working multiple jobs. It's a hard grind but the payoff, well, pays off.