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The recommendation by health professionals to eat more vegetables should not be interpreted as the extremes you describe. They mean more than people in Western nations are typically eating now (like just what comes on a burger). Everything in moderation!
If you’d like links to reputable nutrition resources, I’m sure the group here would be happy to share their favorites.
For calorie-dense vegetables like potatoes, beans, and grains, that would be fine. But there’s an upper limit to how many calorie-sparse vegetables (like lettuce and plain carrots) you can eat. Too many of those and it would be difficult to reach your calorie requirement (and also difficult to poop). There’s diminishing returns for any nutrient. Your diet should be “well balanced;” advice to eat more vegetables only makes sense if someone needs to eat more vegetables to achieve a “well balanced” diet.
That is an unhealthy extreme. Are you training for competitive eating? Are you on some sort of raw vegan diet? This amount of high volume, low density food is going to stretch your stomach and may make it hard to become satiated on normal amounts in the future.
You should also look into how those vegetables need to be prepared to avoid poisoning yourself. There are lectins in green beans and broccoli that can cause some rough symptoms if over eaten. I’m pretty sure you just have to properly cook the veggies to eliminate those. But, if you’re eating an extreme amount of them daily you may be at risk regardless.
Also, similar to the other answers just be careful. Too much of a good thing is often bad in the end.