The biggest downside of ditching Windows is losing that comfort zone where everything just works without thinking about it. But if you're cool with putting in some effort to learn new stuff, Linux will feel way snappier right from the start.
Since you've got an Nvidia GPU, I'd definitely go with CachyOS - it's been my best Linux experience for gaming and daily use. The Linux community respects it too: https://cachyos.org/
For your setup specifically, you'll probably like how much less space Linux takes up compared to Windows, plus it's way lighter on system resources so your older hardware should perform better. Gaming works surprisingly well these days thanks to Proton, most stuff just runs.
You could dual boot first to test it first without committing. CachyOS would be perfect for what you're doing.
I just moved to mailbox.org for my mails.
I've been trying out Ente Auth as my 2FA, it's also open source with a pretty ui.
And for password manager my goto is currently bitwarden, you get all the features you need for free and it's open source.
Trying to convince my family to do the same feels impossible, they don't care about this stuff lol