Building Durable Raised Garden Beds: What Materials Work Best?

Hey everyone! I've got a question about raising garden beds. I moved into a house a few years ago that had these large raised beds, but they're starting to fall apart. The wood's rotting, it's bursting out in places, and the screws are pulling through. The beds are around 2x2x4 high and shaped like big Ls, but without any bracing.

I have dreams of constructing some sturdier beds, but I need some advice on the materials and construction. What types of fasteners do you recommend? I've only seen deck screws used, but are construction screws a better choice? I rarely see bolts and washers—are they too pricey for this kind of project? I feel like they'd help prevent screws from pulling through.

Also, how do I brace these beds properly? Mine has no bracing, which has led to the wood pushing out over time with the soil being worked. I've tried temporary fixes with metal bracers on the 2x4s. Are those effective, or should I be installing horizontal 2x4s on each side? Is there a rule for how many bracers to use per foot?

Lastly, any general tips for building long-lasting beds from seasoned veggie farmers would be much appreciated! Does the local weather significantly impact durability? I'm in Ontario, facing cold winters and hot summers. And how important is the type of wood? Would cheaper wood with deck screws be sufficient, or should I invest in rot-resistant wood for using tougher fasteners? Thanks a lot!