Many things that were conceptually conceived in the 20th century didn't become viable until the 21st, such as OLED, VR and AR, raytracing, telesurgery, a whole slew of types of artificial organs, a gigantic amount of miscellaneous advancements in integrated circuit fabrication, alternative vehicle fuel such as methane, hydrogen and rechargeable batteries; maglev trains, innumerable safety improvements in aviation, mRNA vaccines and so on and so forth. I don't think it's fair to credit all that stuff to the 20th century, unless someone somewhere saying "be real cool if we could do that" counts as inventing something.

That is pseudonymity, not anonymity

No, "overwritten" data doesn't actually get erased right away due to wear levelling. As SSDs get esoterically smart with how they prevent unnecessary erase operations, there's no way to be sure without secure erase.

A special feature known as SSD secure erase. The easiest OS-independent way is probably via CMOS setup – modern BIOSes can send secure erase to NVM Express SSDs and possibly SATA SSDs.

There's no modem needed, actually. All of that can be done in software, and you can configure a desktop as a PPPoE client (that's the protocol your router uses to log into your ISP's network and receive internet connectivity). Obviously, you'd need to configure that PC as a router for other computers to also share the connection, and running a typical interactive system 24/7 as a router is hideously inefficient in terms of power use.

If you're supporting someone on Patreon, you're not really purchasing their content from a third party, are you?