Need advice on mobile speed optimization (2-month-old site, CWV issues)

Hi everyone,

I’m looking for some advice on mobile optimization for a website I built myself about 2 months ago.

Despite decent early rankings, my mobile loading speed is noticeably slow when I test it on my phone, and I want to fix this since I know Google prioritizes mobile-first indexing.

Here is a breakdown of my current situation and site specs:

Current Rankings:

• Keyword 1 (Primary): Solidly on Page 1.
• Keywords 2 & 3: Fluctuating between Pages 1 and 5.

Site Setup & Content:

• Platform: Imweb (a Korean website builder). I’ve also implemented some custom HTML.
• Images: The builder doesn't properly support WebP, so I've been using heavily compressed PNGs for all my images.
• Content: The site has numerous categories and a large backlog of blog posts. I am currently publishing one new blog post every single day.
• Backlinks: I’ve been sourcing backlinks through Fiverr. They are being published steadily, and I believe they are of good quality, so I don't think my backlink profile is the issue here.

PageSpeed Insights (Mobile):

• Performance: 54
• Accessibility: 79
• Best Practices: 96
• SEO: 100

My Question:Given that my mobile performance score is quite low (54) and it visually loads slowly on my device, what specific areas should I focus on fixing to improve my mobile optimization? Considering my builder's limitation with WebP, are there other workarounds I should be looking into?

Any insights or recommendations would be greatly appreciated. Thanks in advance!

Defer non-critical CSS and JS. Inline only the critical CSS needed to render the above the fold content and load the rest asynchronously.