Fedi, recommend me a time tracking program without bullshit.

Current use:
I have a text file on my desktop called today.txt. At the top is this:

Mon xx
Tue HS
Wed II
Thu ER
Fri VP
-------
VP: Arcade steady
II: Improbable Island
HS: House Stuff
PF: Pinball freelance
ER: Errands
xx: none of the above

and I just note down what I did that day, and underneath is today's date and what I wanna do today, and then what I wanna do this week, and this month.

This setup is fine and it works and there's no fuss at all, it takes me two keystrokes at the end of the day to say what I did, BUT, remembering what the hell I did last week is an Issue.

Difficulty level: Linux and Android. I don't want to open a terminal. I don't want to mess about telling software who the client is, I'm the client. I wanna click a couple things and be Done. I'd like to do this on my phone as well if possible, I have a Nextcloud setup and can sync arbitrarily from my desktop to my phone if the program exposes its data files. I'm not giving anyone my email address or signing up to any online web app, I want a program for my computer.

Bonus: show me a coloured-in calendar with the various Things Wot I Did in different colours.

As simple as my today.txt, but it records back further than a week. Ideas, go!