Thank you, sorry it took awhile to get back to you, I just saw the notice.
First, just because a chromebook is past its EOL doesn't mean it is vulnerable. It's still a lot safer than any Windows with antivirus.
One of the YouTubers I watch is Switched To Linux. He is really into security. He uses a distribution called Tails. He has thumb drives for each bank/financial institution, etc.
Here is the link to get you started.
https://www.youtube.com/watch?v=VLFFSPRiQo8
There are compatible spreadsheets in Linux that you can import from and export to Excel.
People talk about doing a dual boot with Windows, but Windows sometimes takes over and doesn't play well with Linux.
Just to be clear I use a Chromebook 99.9% of the time and never worry about getting hacked. Since everything is on the cloud, you should know that all files on the cloud are encrypted. I use Linux when I come across something that makes it easier to use.