Flameshot works pretty well for me. With some tweaks in the settings, I was able to get it really close to how I used sharex. I believe it has upload, but not the gallery, but you can always use your file manager for that. I'm also not sure again about the link history but I'd recommend checking it out when you get the chance and tweaking it to fit your needs.

ddg gets its results from bing, I'd recommend startpage if you want google results while being privacy respecting.

Then, would it be a better idea to create one mega-fediverse app that combines but also separates all the different features of each platform (eg: when viewing it on a browser, it would have a Lemmy tab, matrix tab, mastodon tab, etc) and then have the functionality and format be separate for each one of those instead of trying to pull a "can do everything, good at nothing" type of platform? That would solve the email issue, but I feel it would be more complicated to implement but I've also never developed anything remotely like that ever and so I'm not qualified to speak on it.