My time capsule no longer backing up under Catalina 10.15.6

It might be coincidence by this all happened when I moved to Catalina OS 10.15.6, but was ok in previous version of Catalina.

More likely you were just lucky to get away with it that long.. 10.15.5 is when lots of new people got added to the lists.

Catalina has determined it needs to create a whole new backup. The why is very obscure.. but now that it has happened you really need to figure out how to move forward which is not easy.

I was under the impression it automatically deleted backups, which it must as it Time machine reports oldest backup is 26th May 2018, yet does it delete enough space to generate the new required size ?

That works as long as you never upgrade or install large patches. In fact for ages now the issue is Time Machine cannot figure out what to delete to reduce the size of the backup because it does not have enough details on which files are essential and which are not.

Failed backups also create havoc. The fact that you attempted to backup by excluding the user files just leads to making the old backup less usable.

how do I release some of the older backups on the time capsule if OS is now unable to do this ?

Attempts to do this yourself are specularly unsuccessful. Don't bother.

You need to wipe the existing backup/s and start over.

If you wish to retain the history you can archive the existing backups. Airport Utility disk tab offers archive.. so plug a standard Mac formatted USB drive 3TB or larger, into the TC and archive.. it will take 1-2days.

Then you can start over.

Or just shrug.. consider that old backups for a working computer.. to which you are doing the right thing by creating a new backup will be unlikely to help in the future.. just do a quick erase of the drive and start over.

However Catalina is having issues backing up to network drives.. especially the Apple Time Capsule.. which is now out of date since Apple moved protocols for network to SMB3. TC only ever supported SMB1 which is now a security risk and deprecated across all OS.

We are strongly recommending people use Carbon Copy Cloner or equivalent 3rd party app for now.. big sur might finally invest in updates to Time Machine.

My Airport Time Capsule has been backing up daily since 2015

On a more general note.. 5 years on a TC is pretty well its economic lifespan. Hard disks do not last forever and the risk of total failure is increasing daily. You may like to consider moving to other ways of backing up.

Apple got out of the business. For now the best, cheapest and most reliable solution is a USB drive plugged directly to the computer as you are doing.

For networks a NAS.. synology for example is best.. but they are expensive.

Performed a archive copy of the TC to external USB, sizes are the same, but the USB version only loads up a NOW backup and all previous dates are not there, but there are on the TC ?

You need to leave it running in Time Machine for spotlight to reindex the backup.. might take an hour or more.. if the backup is large.. then a long time.

If the sizes are the same then all the files are indeed there.

At the last resort you can access them manually via Finder.. not recommended but possible.

Say just all those dated 2019 & 2020 and the "Latest" directory, is there anything else maybe hidden I need to copy?

and give it the same structure

Backkup.backupdb

- Ian's iMac

- 2019-01-29-021238

- others ect.

You cannot just snip off bits of the backup. The end result is that it won't function. You might still be able to dig out files but truly not worth the effort.

Also you will have issues doing it.. I have tried and it keeps giving format errors, even when the disk is correctly formatted.

Not sure what you gain doing this. Yes it will use less space but it will only be required until you build up a few months worth of backup anyway. Then you can wipe it and go back to using your normal backup.

And yet there is a "Time Machine Backup" ???? from 2018-05-26 to 2020-08-13

I am rather confused,

Could I not copy this to the external USB for safe keeping ? and then wipe the TM

You are looking inside the backup.

On the TC a backup is stored in a sparsebundle. This is a virtual disk. When you mount the sparsebundle it opens and shows the contents as a second mounted disk.. Time Machine Backups.. i.e. you have the TC disk and separately the virtual disk but they are both the same thing.

You can attempt to backup the main backups.backupdb to your USB drive directly. I think you will run into problems. Just as mentioned above it will not allow you to copy it.

I will have a go and see if you can get around the copy protection.. but I doubt it.

Try opening the backup in Finder.. drill down until you get to the dates of all the backups and then see if you can open each one..