Don't be too obsessed with the scores in Google Console, or any other tool.
The only question is how fast (or slow) your site loads for real users (since this impacts the user behavior and bounce rate, and that's what counts for Google).
For example, I score F in almost all tests and tools, or "slow" in Google Console, since I have some slow loading ads and elements on my site. However,
the primary text content loads fast as a lighting, and I definitely don't lose any visitors for a slow site. And I am ranking as a king as well

.
This proves to me that all these ratings by tools are way too over-hyped.
However, if your site really loads slow for the real user, then you should analyze it in detail and find the reason (which can be many, and impossible to tell unless we know your site)