AMD drivers: use the built-in MESA drivers that include the official AMD support.
Gmail: ProtonMail for the service, Kmail for the desktop client.
Chrome: Firefox, or Librewolf if you care about privacy.
Office365: LibreOffice for full FOSS or OnlyOfficr for less freedom but more comfort.
iTunes: depends entirely on what you use it for, but I buy my music mostly off of BandCamp these days.
MuseScore: MuseScore
Norton: Why were you using Norton in the first place? It's practically a virus itself. If you need an antivirus on Linux, you might want ClamAV/ClamTK for something that runs locally only, or Microsoft Defender for Linux.
Py-Charm: Py-Charm, VSCode, Vim, Kate/KWrite
Remote Desktop to iOS: I got nothin'
Star Citizen: Star Citizen
Steam: Steam
VPN: Wireguard
Windows Games: install locally using Wine and then add to Steam as a non-Steam game to use Proton for better support.
Windows 10: run it in a VM if you still need it, or keep it on a separate SSD and dual boot into that.
After completing the challenge and making sure your system is usable and can survive a reboot:
If you've kept the old package manager, search for installed packages and make sure that the package manager itself is the only thing left. Then delete it.
The beauty of this exercise is you can make it as easy or challenging as you want just by changing the targets, and finding different combinations can keep things interesting.
As other commenters have said, its about as strenuous as doing two normal installs.
However, if you want to do this challenge but feel guilty about the consumed resources, consider donating to the two distros you are performing this with to cover any additional service costs. In all likelihood it'll only cost them fractions of pennies, but any reason to donate to FOSS is always appreciated.
This goes against the spirit of the challenge, but as its a singleplayer game (unless you bring friends and SSH!) you can definitely choose to allow dd, chroot, and similar tools
The pinetime using infinitime basically does that, albeit without always on and the heart rate monitor only fires off when the screen wakes up or when you go into the applet and click start. But i usually get around 2 weeks of battery life with it, maybe more.
Its probably not as good as this, but on the plus side, it's like a $25-35 watch before shipping.
It would depend on how critical the data is and if the cost benefit analysis breaks even or tips in favor of the moon. I would imagine housing state secrets up there would be reasonable, and documents (text files) don't take up a huge amount of space. Video would be more challenging. But realistically you could probably store all of the Secret and Top Secret documents across a few servers with maybe 5 drives in a RAID config each. Probably even a single NAS-like solution.
Kmail is simple and to the point, and at least in my experience is easier to set up. Bonus, if youre on KDE, it integrates very nicely.
It's also more performant than Thunderbird.