Every alternative I've been able to find has been either poor quality or too shady for me to ever actually want to use.
You can set it up yourself really easily (got it running locally on Mac in 5 mins), throw an auth'd gateway in front of it to keep it away from bad actors: https://github.com/mozilla/send
Now that you've made a start you'll probably find you start adding services to that box under the stairs. Why pay for Dropbox when you can use your very own box with far more storage for far less money? Run something like Airsonic and you can stream your own media. Instead of having Xi Jinping watching your goldfish through that IP camera you can put the thing in a dedicated network zone, run a VPN on the box and make the camera only accessible through that VPN. The possibilities are close to endless, the costs are low and coming down all the time, power consumption can be negligible if you choose the right hardware. If in the end you don't like running your own services you can always use something run by someone else so why not give it a try...
Managing backups and data integrity is no joke. Almost everyone does a shit job and don't know it until the data is gone.
All that just for few hundreds of euros; all data are private and nobody is trying to constantly upsell or trying to figure out how to monetize something taken for granted until now.
If you have family or friends you can make a deal with them: you get to hang a backup storage device off their network, they get to do the same on your network. Send encrypted backups and your data should be safe, and so should theirs. Problem solved, everyone happy and nobody gets to mine your data.
have you tried https://catbox.moe/ (or others https://archiveteam.org/index.php?title=Pomf.se/Clones)? Not sure what you mean by "shady", but most of them provide a direct download without any interstitials.