Vegetables are notoriously difficult, particularly by displacement method. You could use a sink or container full of hot water to soften the bag and help you get the air out. Another common way to stop floaties is to pack something heavy but non-reactive in with them. A stainless steel dinner knife or two seems to be a popular option.
There’s an entire thread devoted to floating bags on here somewhere.
Here is one such thread, though this is not the one I was looking for:
This is the one, I think, from forever ago:
And something from about a year ago that specifically pertains to vegetables: