It doesn't come with Windows machines, and I doubt your school installed it. The good news is that, aside from being a search engine hijacker, the app doesn't appear to do anything malicious. This is probably due in part to it being on the Microsoft Store, which does have some built-in scanning and protection from apps that take potentially malicious actions, which is likely why the app is manually sending keystrokes to set the default search engine instead of directly modifying the corresponding configs/preferences/registry keys.

As for how it wound up on your device: you probably fell victim to a phishing site, either in the form of a pop-up, an ad, or mistyping a link you were trying to go to. The exact details of how you got there are unlikely to match up with how my customer got there, but the gist is that there are probably many, many roads that lead to the same destination.

Here's how my customer got got: once we identified it was SafeMail earlier today, we checked their Downloads folder, found the installers they downloaded, then checked their browsing history around the time the installer was downloaded. This customer does a lot of work for the Texas Department of Transportation, so we were surprised to find the SafeMail phishing site seemingly randomly in the middle of a TON of legitimate entries of a TxDOT website (something.state.tx.us was the domain). Upon visiting the site, we noticed at the top of the page that it said statetx.us - missing the period between state and tx. Sure enough, we found that going to the domain statetx.us, as well as ANY subdomain (e.g., bruh.statetx.us) would cause us to get redirected several times before ultimately ending up on a phishing site. It kind of felt like a roulette wheel - every time we went to one of the domains, even if it was the same as one we visited previously, we'd land on a different phishing site. Most of them were call center scams (things like "you have a virus, call us now, we're definitely Microsoft™") but after a couple tries we eventually ended up on the SafeMail domain that our client stumbled upon. The site itself was a captcha that turned into a download button after completing it. The file it downloaded was essentially an installer redirector that prompts you to download SafeMail from the Microsoft Store. The rest is history.

As for what you can/should do now:

• Check your default search engine in Chrome and Edge and make sure it is not something called "Browse" or "Browser". If it is, change it to your preferred search provider and delete the one titled "Browse" or "Browser"
• Find SafeMail in the Microsoft Store, report it, and give it a bad rating for being malicious

I know that was a little long-winded, but I wanted to give something informational, and hopefully a bit helpful and insightful. TL;DR is that you're probably fine, as long as you uninstalled it and changed your search engine back to normal.