Downgrading macOS Catalina to High Sierra

I had no intention of ever returning to this site. But I decided to do so one last time for the users herein who do NOT "know everything".

My 2015 MBP is still in great shape and it runs flawlessly (and predictably) under High Sierra. My "daily" Mac is an M-class MBP and it is a true performer. (It took 10-1/2 months before I could get it run without immediatly crashing upon loading Safari, however.) I have several critical 32-bit apps that simply will not run under Mojave, and even then they run better under Safari. The most important one is Adobe Creative Suite CS6, but there others as well. I don't use them daily, but they are critical nonetheless.

Many consider High Sierra to be a dinosaur... perhaps it is. And it's likely than anyone else who would use it on a 10-year old computer, would do so for similar reasons... the need for 32-bit apps. Of course, these will still run on somewhat newer hardware (like a 2018 MacBook Pro).

So this final post is for those users in a similar use case, and who also discovered that Apple's Recovery Server would NOT install (or reinstall) macOS High Sierra. You can't even access it from Apple's App Store! As indicated in an earlier post, Apple let the SSL certificate for the High Sierra (and likely other servers) expire. As such, the internal links for the installer would not load the installer, due to a now inaccurate link to it. This completely broke the installer app, with no explanation as to why... for 2-1/2 YEARS! Note that this also prevented users from downloading the installers directly from the App Store.

I am not the one to discover the reason for this error. But I likely am the reason it finally got fixed. Between posts on this site and comment on every page I could find on Apple's Support site regarding "How to download and install macOS".

So, while my obstinance regarding this issue (impacting only a few users) might well have ticked off some of the experts herein, hopely I may have helped out those who might never have found the answer they desparately needed!

Thanks... but READ THE POSTS... ALL of them from the beginning!

I KNOW how to do it... I've been working exclusively on Macs for over $35 years.

If you read the circumstances, the problem was that Apple's Recovery (and the links on the App store) where trying to retrieve the update using an "HTTPS" query. And I attempted to do a clean install... about 20 times! But... Apple let the SSL certificate for the High Sierra (and likely other servers) expire. As such, their utilty could not find the installer. As such, it just there forever, never receiving the file and never quiting.

And explain to me how one can make a bootable installer, without access the the full installer from which to make it? (Never mind... don't tell me, because it can't be done!)

With all due respect, I don't think that is necessarily true. I have, in fact, seen many articles in which Apple had given advice as to how to do it.

Regardless, that does not negate the ability to do so.

I concur with your reply, Phil0124... all of it. Unfortunately, it failed.

I also tried to make a clone of my 2015 MBP, to then use Recovery to reinstall from the clone. I attempted this using a SanDisk Extreme 4TB SSD. It took 18 hrs to clone the drive, then failed at the final step, leaving me with a 3TB SSD. (Fortunately, I was able to reformat it.)

I thought about using a fresh Time Machine backup of the my 2015, then loading the 2018 from that. But if it fails, I might have difficulty returning the 2018 back to Amazon Resale. I do have a current TM backup of the 2018, but you never know. Another concern is that I don't believe Apple still provides the various updates to bring High Sierra from the original shipping version to 10.13.6.

Hi Phil,

I was expecting the 2018 MBP purchased from Amazon to arrive with the macOS originally shipped (High Sierra). Unfortunately it was loaded with macOS Catalina. As I'm sure I mentioned, my purpose for this laptop was strictly for running Photoshop CS6 and other 32 bit apps. As such, Catalina is not an option.

Since I was having difficulty obtaining or creating a bootable copy of High Sierra, I finally decided to just send it back to Amazon. Too much time wasted already.

Having found multiple conflicting descriptions of the process, I had a very long conversation with Google's AI, that walked me through the process of cleaning out my personal data, as the instructions I found were contradictory and unsuccessful. Clearly now, THAT was a mistake! Following his/her/it's (bot's) instructions, I trashed the drive and I cannot get it back to normal to ship back to Amazon.

While the bot was describing the preparation of the drive, it said...

In "Disk Utility"", you will see two partitions: Macintosh HD and Macintosh HD-Data. Select both and click the "-" button and select "Delete".

Yes... that is indeed what it said: "Delete"! Knowing that it didn't sound logical. But after reading it several times, I figured "Who am I to argue with something that cost over $100 billion to build and approx. $85 billion/year to maintain"? So, yes... I DELETED both the User and System partitions.

I have no idea what to do next! Is there a way that I can restore the drive? I sure haven't been able to locate one. At this point, I can't be ship it back to Amazon, per their 1-year window for returns.

You know what? I'm sorry I asked for help here... again!

The issue was real. It had nothing to do with my atempts to recover. The issue ONLY affects High Sierra and no other version and it has been an issue since mid 2023. It's caused by an error in the NVRAM Software Update URL in the macOS High Sierra Install menu, such that the Recovery Server could not be contacted. It would seem that this a vey common issue, but only with the High Sierra Internet Recovery Server. The cure was to modify the code within the installer, such that link to the URL to the server needed to be changed from "https" in to "http". Note that this ONLY affects High Sierra installs.

I won't bother to regurgitate the entire issue and cure. If you are interested enough to investigate the problem and it's cure, then this is the link to the video...

https://www.youtube.com/watch?v=ouNQS36dIBw

Thank heavens I was able to find some who took the time and effort to figure out the answer.

So forgive my audacity for asking for assistance. I promise it won't happen again!

I thought I had already been to that page for the Installer. But, in fact, it was a different page. That looks promising! Thank you.