I don't think we're doomed. I think the solarpunk movement has plenty of valid ideas to address these problems.
I am new to the movement, but it's definitely given me some optimism — I believe that we have the means to deal with any crisis with our technology, evolving understanding of the world, and ingenuity.
I am learning things every day and exploring new ideas fairly often. I don't think I am the best ambassador yet (not even close), so forgive me if I am off-base or not 100% dialed in.
Agriculture is in dire need of reform and revolution. It's unsustainable — we could more intelligently feed the world by blending agriculture with nature (e.g. by discontinuing monocropping and scaling ideas garnished from food forests) and we can explore scaling up vertical farming. We can power this by renewables and utilize wasterwater recirculation.
We can regulate industrial water usage. We can reduce animal agriculture and grow meat in labs. We can expand upon desalination technology (finding a way to derive scalable benefit from the brine and repurpose the salt) and explore other water capture technologies that all account for potential ecosystem disruption. We can make landscapes that retain water, and reforest and reduce desertification where appropriate (e.g. with ideas from the permaculture movement). We can make water pipelines and more sensibly use groundwater, respecting replenishment rates.
We can explore creating scalable synthetic terra preta and we can explore other promising ideas like this reddit thread proposes.
Solar panels are cheap to manufacture, and if we can finish the proton battery technology, we can build scalable, cheap energy storage and power scalable vertical farms — and more broadly power our societies.
I am sure for whatever crisis you can think of, there is valuable discussion in the solarpunk community to explore more nuanced, comprehensive, and educated viewpoints than my own.
You're valid in your perspective, but I don't think I am throwing my hands up just yet. There are billions of people who can figure this out if we actually take the initiative as a global society.