plugins – WordPress web page struggling with performance

I have some experience with building wordpress pages but me and my friend are starting an e-shop, we wanted to have everything perfect without any bugs and problems so we decided to hire a freelancer. He did a great job, we’re loving the page but we’re experiencing some performance issues that drive our seo down.

I’m using web.dev/measure, to check the site almost on daily basis and the performance tab is going pretty crazy there. One day I have 25 score on there, next it’s 80 and then back to 20s… (100 is the best).
I’ve been trying to solve this by some site speed plugins such as NitroPack, ShortPixel for images. At first they seemed to work as that was the time I got 80 on the tool. But today (next day) it’s back at 23. I have no idea what’s going on and I need to resolve it soon so we can get our SEO scores back as I understand performance plays a role in that too. What would you try if you were in my place?

enter image description here

I could maybe contact hosting but that shouldn’t be the problem because it’s a slovak website on slovak hosting.

www.greenstuff.sk if you want to check it or test it on that tool. Any tips or help would be appreciated. Thank you.