Got a better offer, but the timing is tricky. Need advice.

I've been working at my company since 2021 - almost 4 years. I have 5 years of experience (Frontend/Fullstack React) if you can count one year as a working student internship at a previous company. So let's say this is my first job. I worked on the company's "flagship" project from the beginning of my career there until February of this year. In February, the client had budget cuts and had to stop development. Since February, I was on a poorly managed project with an exceptionally annoying client - I wasn't happy.

Recently, that client got funding - I'm back on the project. I will be working with a new developer from the client's side - an experienced guy with about 8 YoE. We will be slowly rewriting our application from scratch because the client made a business pivot and a lot of things need to be overhauled, so the decision was made to write it anew - I guess it's a cool opportunity for growth?

Yesterday I had a job interview at another company. Today I got an offer. Better money, the people at the technical interview seemed okay - they gave the impression of being technically strong. HR in the first interview said that the average employment time at this company is high and people like it - her words were confirmed in the technical interview. The only thing holding me back is that the code in the project I would join is legacy. It is the largest e-commerce application in Scandinavia, divided into microfrontends. The guys said they are improving it on an ongoing basis, but there are services there where, for example, there's still no TypeScript :D.

Do you guys think that changing jobs in this case is a bad idea? Or maybe working with such code will help me develop? I work a lot after hours, I study a lot and I think that's why I'm moving forward somehow, but at my company, until now I've felt a standstill in my skill progression. The situation might change now because this greenfield project is starting... I don't know what to do :)