First up, great to have you onboard and I'm really glad to hear that TurnKey has been useful to you so far. Thanks too for providing all the info you have, makes it easier for all of us. :)

This gives me warnings that both MariaDB and PHP are now deprecated.

FWIW both the MariaDB and PHP versions in v17.x will continue to recevie security updates and generally be supported by Debian (the base of TurnKey) for quite some

So I have 2 responses to this.

Having said that, Nextcloud tends to move fairly quickly and often stops supporting older versions of dependencies - PHP in particularly. So I'm assuming that when you say that they are "deprecated" that is in the context of Nextcloud specifically.

From time to time, I have logged into the container and also done a apt update/upgrade - this may possibly be counterproductive?

You don't really need to do it as TurnKey auto installs security updates every 24 hours. OTOH it certainly won't (at least shouldn't) do any harm.

But as you've noticed, it doesn't actually give you a newer version of the specific software. It simply pulls in the latest patched release (i.e. bugfixed) of the same version.

I saw somewhere that there is a turnkey 18 somewhere - how do I upgrade to that version? And will it upgrade MariaDB to 10.6

Yes, there is an updated appliance - currently v18.1.

You have a number of options to update/upgrade to the new version. The appliance upgrade doc page has some relatively general info which might hopefully be of some use?! FWIW it also gives some more context to the apt package versioning.

To summarize the 2 main options covered in the docs; and add one more:

1. Launch a new v18.1 server and migrate your data using TKLBAM.
2. Leave your current server as is and do an "in place" Debian upgrade (i.e. upgrade the base distro to 12/Bookworm).
3. And the other Nextcloud specific option - manually migrate your files and database from your old server to a new v18.1 server.

1. TKLBAM

As noted on the TKLBAM page, there may be some manual post restore tweaks required. But hopefully not too many (if any) as you're going from one major version to the next one.

The beauty of migrating your data to a new server means that you can keep your current server running until you are happy with your new server. Even once you move to your new server, you could just stop the old one and leave it there for a week or 2; just in case...

It does require registering for a TurnKey Hub account, which in turn requires and AWS account. Also by default, it will backup all your files and upload them to AWS. Depending on how many files you have and the bandwidth of your internet connection, that might take a while. And then you will need to wait for it to all download again to restore your data to the new server...

OTOH, you will then have an offsite backup of all your data, ensuring that it stays safe and sound, even if things go really pear shaped. AWS storage fees are relatively cheap (IIRC ~$0.023/GB/mth) so unless you have TBs of files, might actually be something that you want but haven't considered or got around to before?

The need to wait for the upload and avoid the immediate download altogether (until you actually need it) can be resolved pretty easily. TKLBAM can also just create a local backup, which can be directly copied to the new server and restored it again with TKLBAM.

2. "in place" Debian upgrade

I don't have much to add in addition to the doc page linked to above. I wouldn't expect it to be particularly problematic or painful. But if it does go pear-shaped, it will likely trash your server. As noted on the doc page, while we don't officially support that method, we will still try to help you out if you have problems.

3. Manually migrate Nextcloud files and database

While I don't have much specific info regarding this path for you, with some basic Linux skills and a bit of "google fu" this approach shouldn't be too hard. Again it's not a "supported" path, if you hit issues, I can try to help out as best I can...

am wondering if it would help performance to split the install between solidstate for the OS+Appliance and spinning rust for the data files (the "dropbox" part of NC)?

I imagine that might help. Assuming you are running on Proxmox, probably the easiest way to do that would be to launch a new TurnKey server with a root volume located on an SSD. Then add an additional volume located on a spinney disk and mount it somewhere - I tend to create new appropriately named directories in /media - IIRC that needs to be done on the host too? Them move your files to the new volume - I recommend stopping services such as Apache and MariaDB while you do that. Then finally bind mount the new directory to the default location that Nextcloud expects them to be - and restart services.

Good luck and please post back regardless how you go. If you go well it'd be great to hear and anything you can share from your experience will be helpful for others I'm sure. If things don't go as planned, hopefully I'll be able to help out.