I see a few red flags here. The problem is, I can tell you what my expectations are when I hear this, but I have no idea what their expectations were. So it might be totally wrong. Or not. In absence of the others, you are the only one in the position to judge that.
Anybody changing jobs working for a new company needs some time to get used to their way of doing things. And in case of software development, their core business. Likely, they aren't developing software for the fun of it, but because the software is a tool for their core business. Software developers switch jobs and land in companies with different core businesses, and need to learn about those. No matter how good of a software developer you are, if you switch from developing a scheduling software for warehouse worker shifts to developing a software about insurance comparison and rates, you will be new to all this. It takes many months to get accustomed to a companies core business, that is normal and expected.
When I hear "senior X", I take that to mean that there are roughly 3 levels of "X": "junior X", who need help with their own jobs, "normal X" (often without any prefix, just "X") who can do their own job just fine without any help, and "senior X", who are so good and experienced at their job, that not only can they do their own without problems, they also have the capacity to help a few juniors with theirs at the same time.
To be honest, most people I know are barely at the "X" level at 6 years experience. Sure, they don't make any foolish beginner mistakes any more and they know how to get help from documentation and Stack Overflow when needed, and they do a "good job". Solid. But they are still a long way from being so efficient and knowledgeable that they could do a solid job and teach others.
So what likely happened was that the team said "hey boss, this is just too much work, we cannot possibly complete all of it in the timeframe you are looking for. We need more developers." And the boss decided to bring in more developers, because they did want to get it all done. And they hired a "senior full stack engineer". However, whoever hired you thought that not knowing most of that "full stack" tools they use was good enough.
However, knowing your tools is a big part of being a "senior". Without knowing your tools, there is no telling whether you actually are (or would be) a senior.
So the team, who had been told a senior would come and help them, get a person that is in no position to "do their own job and help others". The new hire needs help doing their own job. Not because of the unknown core business, that is understandable, but because of their non existant knowledge of the tools used. In the above terms, they got the equivalent of a junior.
There is not really anything they can do about it.
There is not really anything you can do about it.
The best way is to sit down with your boss, both you and the team, either in seperate sessions or combined, and explain the expectations. Then consolidate them into a working thing.
If you were hired with the expectation that you need time to learn the tools they use, that is something the team needs to know. They can probably accept that. Since you already have the experience, you will go from junior to normal to senior in maybe a year or two, not in ten years like a normal junior. But the team needs to adjust to the fact that they did not get what was ordered and that right now they have a junior that needs help.
If you were hired by mistake, because the person doing the hiring just didn't know how to do their job and check whether you knew the tools, then that is a big problem, because if they don't have the budget to hire two people and they need a senior now, they may have to let you go. That is on the person hiring you and not your fault, but the fallout will still hit you, not them.
Take the meetings, see what unfolds. But it might be time to look for another job, that is actually tailored to your specific strengths, to the things you already know and are becoming a "senior" in. Or, if you want to switch technologies, look for a non-senior role, where the expectations are set that you need to learn those new things. It is your responsibility to find out if a job is just that, just as much as it is theirs to find out whether you fit their requirements.
