Saving Medium blogs and Twitter threads locally just doesn't work, so I've pretty much stopped reading Medium and treat Twitter as purely ephemeral.
From what I could gather, Twitter’s bookmarks have a limit and it deletes the older but it’s not said out loud.
As for Twitter, you can bookmark a link to the tweet, but it won't parse a Twitter thread for example. Same applies for thread compilers (like https://threadreaderapp.com/).
Probably the biggest annoyance with Pocket is that you can highlight stuff, but you can't export your highlights. It has an API, but it doesn't support highlights. Contacting them about that resulted in something like "we're a small team and have no API expansion updates we're willing to share right now" (paraphrasing). They also protect their sign-in form with Google's Captcha, making it non-trivial to scrape that info. The best option I found (https://github.com/karlicoss/pockexport) requires fiddling with browser's dev tools to get the consumer_key, but I couldn't be bothered to get that to work.
Memex (https://getmemex.com/) just gives you a browser extension that allows you to highlight nearly every text on desktop, but becomes completely useless on phones (they're too locked down for something like that to work).
I was also frustrated by their API not supporting highlights, I emailed their support and they replied exporting highlights is a good idea (Yes, Einstein) and they'll consider it. I love pocket TBH but this is really a PITA. So I spent sometime dabbling to create browser extension that let me copy highlights to clipboard, and ended up tuning down to a bookmarklet. Let me know if you want to try it, I can put it somewhere and will share the link.