Is it super unsafe to keep running High Sierra on my 2017 MacBook Air?

Given the recent Apple vulnerability, I was looking to upgrade my system but don’t actually see an option to, I’m assuming because I bought the is computer in 2018. I’m not very computer savvy and only use the computer for basic items, but I do online banking, etc so just wanted to see if it was a really bad idea to keep using this computer given high sierra is no longer supported! Should I upgrade it to something even if I can’t upgrade it to the most recent system? Buying a new computer now really isnt an option… I appreciate any advice, thank you!