Should I update MacBook Pro (Late 2011) to El Capitan or Sierra?

Hi Sarah, welcome to the forums and Macintosh, and warm greetings from a hot Australian summer's day.

The Mac can go as far as macOS High Sierra 10.13.6. This OS had six updates to bring it from 10.13 to 10.13.6 and Apple offers the installer for 10.13.6 at the download page for old operating systems here.

To get to High Sierra for your sister's Mac would be a two-step process, first to a point at which the High Sierra upgrade can happen, and then for the High Sierra upgrade itself.

So from Lion you can get as far as macOS Sierra 10.12 and from there the last jump up to High Sierra 10.13

Given the age of the Mac you and that it is still a very serviceable computer I'd take it as far as it could go. Co-incidentally I had a reason to startup a very old Mac yesterday with 10.5 Leopard and poked about with Safari - it was so old that it could load very few web pages mostly due to it's inability to comply with all sorts of modern requirements, security among them. The same will start to happen if you leave your Mac at Lion, or even Sierra.

Most on these forums would also recommend browsers other than Chrome. If she didn't want to use Safari there are many other options, Firefox is a well-known one but by no means the only, and indeed there are "better" browsers out there.

The installers for the earliest three systems on the page I've linked above will provide a compressed installer - a .dmg file - to your computer. Run this then when the Mac restarted to the newly upgraded system click the link (using Safari) for High Sierra. This will open the App store page for High Sierra which you can't find by searching. This will download the installer when then has to be installed to apply the upgrade.

I have a couple of semi-retired 2011 MacBook Pros with 10.13 and they are doing very nicely, however your sister will have to start thinking now of an upgrade path for a new Mac. High Sierra won't be updated and sooner or later will be less than is required for the internet and general software needed for daily use. But for now I hope she enjoys the system when your job is done.

Lastly, please make sure she has a backup of the Mac. If she doesn't already she should immediately get an external drive (obviously larger than her Mac's drive) and create a Time Machine backup. It secures her data and is the first step in transferring it to a future Mac she will acquire.

do you think Web browsers will be supported on High Sierra for at least a few more years?

Pure guesswork, but a qualified yes. For example, I had to upgrade my mother's 2009 iMac from 10.11(El Capitan from 2015) to 10.13 (High Sierra from 2017) because she was reporting that Safari spat the dummy on a lot of websites important to her. I had a look and found that under 10.11 the browser was no longer capable of doing what she needed, chiefly internet banking. After the upgrade to 10.13 - which like your sister's Mac is as far as it could go - it was motoring along. However, that was one year ago...

Safari depends on technologies in macOS, but third-party browsers are less reliant. So if the OS can't be updated to adapt to changes then Safari falls behind too. As you saw with Chrome, all browsers have their sunset clause on any system too and, dare I say it, start from behind Safari (IMO) but gain when Safari can't be updated yet can hang around for a bit longer on an old OS.

Considering all that, the life of a computer was considered to be about five years (three in businesses), but Macs generally last much longer, certainly longer than a cheap PC box. The longevity bequeaths the problem of out of date hardware, though for many people who don't thrash their machine it isn't a great issue. Apple historically, and still now, pushes the OS software all the time and is not afraid to escort old hardware out of the building if necessary when it comes to a new OS.

Time Machine is one of the unsung heroes in macOS. Not only is it a painless backup regime built into the OS, but the migration of data to a new Mac is equally painless. It's set and forget, open a can or two of Kilkenny and come back in an hour and job done. It's never let me down with any of the multitude of my family's Macs and I've been using it since it was introduced into the system in 2007.

When your sister buys an external drive (SSD preferably) it will probably be formatted for Windows. It would be best to reformat it for Macintosh. Apple's guide here will see you right. She will have to use Mac OS Extended as the format. This is the old file system used by macOS 10.12 or earlier but will still be fine to use after the upgrade. I'm using that format on a drive I've had for a while for my Time Machine backups. I'll reformat it at some point, but it's okay for now.

These forums are for all users, not just the experienced users. Return for any question you might have and you'll get a response. Some of them might even be useful : )

Slán

David