There is a lot of evidence that the nutrition in frozen can be better as it's frozen at time of harvesting and not sitting around (including in your fridge). The main issue with frozen veg are that the texture and taste can be impacted, so ti does depend on what you want it for.
eg frozen spinach - genius invention and I always have a bag in my freezer. But, it's not great as a standalone - eg I wouldn't use frozen spinach if I wanted a nice bright, lightly wilted bed of spinach for a lovingly cooked piece of fish. But for soup, pies, to mix into other things... absolutely.
I don't think I've ever bought fresh peas in my life. Similarly edamame beans. Green beans can be good frozen too.
Frozen corn - delicious and easier than cooking fresh corn unless you want to serve corn on the cob.
I'm South African. Frozen carrots were great growing up but I've yet to find a brand here where the carrots don't cook out rubbery. I thought it was just my memory but had some back home last time I was there and they were great. Just not so much here. Maybe it's just me.
Frozen onions, ginger, garlic etc - super handy.
Frozen stir fry ingredients - great although I don't use these often due to space issues. It's easier for me just to slice up a bunch of peppers.
Cauliflower and broccoli - can be okay. Particularly useful if you have small kids for whom these are two of only 3 vegetables they eat.
Frozen fruit for smoothies are good and much cheaper than fresh.
I don't buy much of this but I think tinned fruit can be a good option. I usually have a tin of cherries in the cupboard for emergency desserts - and they work well in a crumble. My dad always has tinned peaches around.