Democrats aren’t losing, they’ve over performed in just about every election since 2020. The party has grown more left wing in recent years but obviously work still needs to be done. Virtually every progressive in government will endorse Biden for reelection. There was no significant primary challenge against him.
If you don’t vote you aren’t participating in an election where you can influence the outcome. In reality the statement you make by sitting out is that you don’t care what happens.
There are valid criticisms you could make of Biden especially over how he has handled the Gaza war. But pretending that you’re enlightened by not voting and effectively helping Trump is not an effective strategy in the long term.