A more lightweight browser?
You gotta understand, browsers are designed to be HTML parsers. You can write an HTML file and double click to open in browser so your only option is a web browser.
Some browsers are certainly light weght than others, find the one that suits your need and use it
There are no shortage of encryption software in the market, use one, any one, Veracrypt is fine, so is million other software for this.
Use a note taking app like Joplin, Obsidian, though not open source is just as fine. Sync its data folder to the encrypted vault created with encryption software of your choice, and you are good to go
Linux clock app?
pyqt5 or tkinter
The answer is absolutely yes
Keep in mind that RSS is just some XML sent over HTTPS connection. For anyone outside, it will look like gibbirish, they can say you are requesting and getting some things from that particular site but not what it is.