What Was Happening
The MacBook had been running an older macOS version that had stopped receiving security updates. The user wanted it on the latest supported version to get back on the security-update path — but didn’t want to upgrade blindly and lose access to applications they used regularly.
That’s the right framing. macOS upgrades are generally reliable, but they’re not free of trade-offs. Older applications can stop working. Some workflows depend on features that change between versions. The right approach is: check compatibility first, back up second, upgrade third.
Our Diagnosis
Step 1 — identify the maximum supported macOS for this model. Apple maintains a list of supported devices per macOS version. Every Mac has a generation cap beyond which it can no longer install new macOS versions officially. For a MacBook Pro 15-inch, the cap depends on the specific year and chipset:
- Older Intel models cap at older macOS versions
- Mid-life Intel models often support up to a specific version that’s now a few versions behind current
- Apple Silicon models support the current macOS
We checked the System Information → Hardware Overview to identify the exact model and looked up the maximum supported version. That number set the target for the upgrade.
Step 2 — application compatibility check. Reviewed the user’s installed applications:
- Critical applications (the ones the user uses daily) — looked up the developer’s compatibility statement for the target macOS version.
- Older applications — flagged any that were 32-bit only (which stopped working at macOS Catalina) or had been abandoned by their developer.
- Productivity suite — confirmed Microsoft 365, Adobe Creative Cloud or whatever else the user depended on had supported versions for the target macOS.
In this case, all critical apps were either current or had a current upgrade path. No compatibility blockers.
Step 3 — free disk space. macOS upgrades need substantial free space — typically 20–30 GB during the install, sometimes more. Verified the MacBook had enough headroom. If it hadn’t, we’d have done a disk cleanup first.
Step 4 — Time Machine backup. This is the non-negotiable. Even on a routine upgrade, having a complete backup means any upgrade-related problem has a clean rollback path. Full Time Machine backup taken to a workshop external drive, verified before proceeding.
How We Fixed It
Software Update. Opened System Preferences → Software Update. Selected the target macOS version (sometimes shown directly, sometimes available via Apple’s installer download page if not offered in Software Update). Downloaded the installer.
Pre-install checks. Disabled FileVault temporarily on this Intel Mac to speed up the install (re-enabled afterwards). Disconnected non-essential peripherals. Plugged in to mains — never run a macOS upgrade on battery alone.
Ran the installer. Followed the standard installer flow. The MacBook restarted several times during the install — this is normal on a major macOS upgrade. Total install time was around an hour, with the firmware update riding along as part of the process.
Post-install verification:
- Login successful, user account intact
- All user data present in Documents, Desktop, Pictures, etc.
- iCloud synced back up correctly
- Mail accounts intact
- Each critical application opened and worked normally
- System Information reported the new macOS version and the updated firmware version
- Software Update showed no further pending updates after a few hours of background catch-up
Re-enabled FileVault with the user’s existing key.
Took a fresh Time Machine backup so the user starts the next phase of the MacBook’s life with a clean baseline backup.
The Result
MacBook running the latest officially-supported macOS for the model. Current firmware. All user applications working. Several years of macOS security updates available going forward instead of falling further behind. No data lost in the upgrade process.
Why This Happens
Two big reasons to stay current:
Security updates. Apple releases security patches monthly for the current macOS and the previous two versions. Older versions get fewer updates and eventually none. A Mac running an unsupported macOS is collecting unpatched vulnerabilities every month.
Application compatibility. Software developers eventually drop support for older macOS versions. A Mac three versions behind current can find that newer versions of its key applications no longer install — which forces an upgrade at a worse moment (when you urgently need the application) than a planned upgrade now.
The trade-off: older Macs have a maximum supported macOS. When the Mac is past that cap, the conversation shifts from “upgrade macOS” to either “live with an older version and its security trade-offs” or “consider replacing the Mac”. We tell customers honestly when their Mac is approaching that decision point.
When to upgrade vs when to wait
Upgrade when:
- You’re more than one major version behind current
- You’re on a version no longer receiving security updates
- A specific application you need requires a newer version
- A planned upgrade can be done at a quiet time with backups in place
Consider waiting when:
- The current version of macOS was released within the last few weeks (let early bugs get patched first)
- You depend on a specific older application that you’ve confirmed isn’t yet compatible
- You’re on a model approaching its support cap and an upgrade now would be a one-way trip — sometimes worth doing a clean install to a clean target version rather than upgrading in place
What to do before any macOS upgrade
- Time Machine backup verified working. Restoring from an untested backup is a bad time to discover it doesn’t work.
- Check application compatibility for anything you actually use.
- Free up disk space — at least 30 GB free is comfortable; 50 GB+ is safer.
- Plugged into mains, not running on battery alone.
- Allow at least an hour of uninterrupted time. Major macOS upgrades can take longer than expected.
Local Help in Putney SW15
A workshop second opinion on a MacBook quote is almost always worth the diagnostic fee.
Many MacBook faults that get quoted as full board replacements at less-rigorous workshops are component-level refurbishments at ours.
Visit our Putney workshop (SW15) or call 020 7610 0500 to discuss.