Aperture replacement

The one thing about Lightroom is that I am baffled by the two apps, CC and Classic. Don't really understand why there are two

The Classic version is currently the only Lightroom version, that includes the tool to migrate Aperture Libraries.

I cannot comment on Lightroom as an alternative, because I do not use it. But it is certainly a powerful, state-of the art professional DAM and editor.

I can comment on Photos, however. Photos has not much support for metadata. You can use titles, captions, keywords, but there are no presets for batch changing. Not all metadata can be displayed. You cannot customize the workspace. A referenced library is not well supported. But the DAM of Photos is better than the DAM of Luminar with Libraries, which is nearly none existing.

The editing tools in Photos are a good, basic set, but the brushed adjustments and layers are missing. You will have to supplement Photos by using photo editing extension like Luminar Flex.

See: Notes on Migrating an Aperture Library to Photos for Mac, 2019 version

LR Classic is basically the Adobe equivalent of Aperture. But there are differences, and there is a learning curve.

LRCC is an entirely different application, and if anything, resembles a souped-up version of Photos. It is not as capable as LR Classic.

On the Photos v Aperture question: you don't replace a pro-grade $80 app with a giveaway. Photos is no match for Aperture. But you can, for no cost whatever, try Photos out for yourself, on your machine and see if it fits your needs.

There are several other major alternatives, depending on whether you're shooting raw or jpeg, the volume you're shooting, your preferences for a DAM and so on. This is a not a comprehensive list, but it includes the major apps. They all have free trials of some form so you can explore. Also, Google searches will bring up a wealth of information about each of them.

CaptureOne

On1 Photo Raw

DXO PhotoLab 2

Mylio

Photo Supreme

Which is right for you depends on things only you can know about the kind of shooter you are. Most of us made this journey 4 or 5 years ago. Enjoy it.

The aim is for CC and Classic to achieve feature parity over time. I actually use both. The family snapshots go straight into CC, the raws I manage in Classic, output the jpegs and then upload to CC (and google photos as another back up). Why are there two? The Cloud is why...

As for the tools: CC has all the basics now but not the more esoteric ones, and it's missing any form of plug-in system. That's one of the areas where Classic really shines. Luminar launches much faster as a plug-in than it does on its own, and you can use any other app you choose as a raw processor.

Have a close look at Mylio, though. It flies under the radar a bit but it's very very good. It has good basic tools and is excellent at sharing across devices (and doesn't use the internet to do it, but rather your own home network.) Also very good at working with other apps and has a few nice touches of its own.

Some of us, a small minority, haven’t made the transition to other photo apps perhaps because of the way that we use Aperture. 

In my case, I have two Aperture libraries one for general photos which could be easily transferred, however, the other library is more specialised and makes extensive use of custom fields and the list view. This combination of custom fields with the list view and using smart albums means that Aperture is very good at organising images and the custom field data.

The problem I have (and which I have been aware of for the past four plus years) is that I do not know of any other photo app which will allow me to import custom fields from Aperture and it looks as if most of them don’t allow, or don’t make it easy to create custom fields. In addition I not sure how many of them have a list view.  I have had a look at the web sites of these apps but none of them seem to have the features that I want. If anyone has knowledge of an app which does have these features please let me know. 

Meanwhile I will continue to use Aperture (on a dedicated, non Catalina mac), having copied all of the photo originals on to an external hard drive in case I ever need them if/when this mac dies (I have also copied the custom field data on to an Excel spreadsheet - a laborious task).

If anyone has knowledge of an app which does have these features please let me know. 

That's probably a question posted at a general photo forum like DPReview. Their Mac forum is here:

https://www.dpreview.com/forums/1017

That said, I'm pretty up-to-date on these apps, and frankly I'm not sure what you want is actually out there. So in that case you perhaps need to look at structuring your data in other ways.

Please search the forum, this has been discussed numerous times over the last 3 years.