Am I understanding bridges correctly?

Good Evening everyone!

With the recent hacks, I just want to see if I understand how bridges work.

Let’s say I have 5ETH on mainnet. I want to bridge that 5ETH from mainnet to optimism or arbitrium.

So I use a service like across and move my 5ETH over to optimism.

Now this is where I get fuzzy. If the across bridge gets hacked and drained, is my 5ETH sitting on optimism worthless now?

Or is it only people providing liquidity to the across Bridget that would lose their funds?

I’ve just read that layer 2s are backed by ethereum security and retail should move off mainnet to an L2. But I wanted to understand the risk before really diving in.

Thanks in advance!