I am dealing with the following issue, and haven't been able to figure out a solution. If you can, please advise:

performed wo update. Produced following output:

Downloading update script        [Done]
updating WordOps, please wait...

Welcome to WordOps install/update script v3.17.0

Installing wo dependencies      [OK]
Installing WordOps      [OK]
Running post-install steps      [OK]
Synchronizing wo database, please wait...
WordOps (wo) upgrade to v3.17.0 was succesfull!
Changelog is available on https://github.com/WordOps/WordOps/releases/tag/v3.17.0

To upgrade WordOps web stacks, you can use the command:
wo stack upgrade

To update all other packages, you can use the command:
wo maintenance

... etc.

Seems fine to me.

Then tried, wo stack upgrade, and got the following:

WordOps dashboard is not installed
Composer isn't installed
Your sites may be down for few seconds if you are upgrading Nginx, PHP-FPM, MariaDB or Redis
Do you want to continue:[y/N]y
Adding repository for NGINX, please wait...
Whoops, something went wrong... [..]
Check the WordOps log for more details `tail /var/log/wo/wordops.log` and please try again...

It's off that it says composer isn't installed, as it was installed via WO in the stack. As shown here:

PHP 7.3 already installed
MySQL already installed and alive
WP-CLI is already installed
Fail2ban already installed
Another mta (Postfix) is already installed
phpMyAdmin already installed
phpRedisAdmin already installed
Composer already installed
Adminer already installed
MySQLtuner already installed
Netdata already installed

The log only contains the following:

2023-08-16 03:34:00,765 (DEBUG) wo.core.logging : Setting packages variable for MySQLTuner
2023-08-16 03:34:00,770 (WARNING) wo : Your sites may be down for few seconds if you are upgrading Nginx, PHP-FPM, MariaDB or Redis
2023-08-16 03:34:12,783 (INFO) wo : Adding repository for NGINX, please wait...
2023-08-16 03:34:12,784 (DEBUG) wo.core.logging : ppa_author = wordops
2023-08-16 03:34:12,784 (DEBUG) wo.core.logging : ppa_package = nginx-wo
2023-08-16 03:34:12,784 (DEBUG) wo.core.logging : ppa already added
2023-08-16 03:34:12,784 (DEBUG) wo.core.logging : Adding ppa for Nginx
2023-08-16 03:34:12,785 (INFO) wo : Updating APT cache
2023-08-16 03:34:17,822 (INFO) wo : Whoops, something went wrong...
2023-08-16 03:34:17,833 (ERROR) wo : Check the WordOps log for more details `tail /var/log/wo/wordops.log` and please try again...

So, I then did a manual update of the apps, sudo apt-get update. That also failed, with following output:

Hit:1 http://azure.archive.ubuntu.com/ubuntu bionic InRelease
Hit:2 http://azure.archive.ubuntu.com/ubuntu bionic-updates InRelease
Hit:3 http://azure.archive.ubuntu.com/ubuntu bionic-backports InRelease
Ign:4 http://mariadb.mirrors.ovh.net/MariaDB/repo/10.1/ubuntu bionic InRelease
Err:5 http://mariadb.mirrors.ovh.net/MariaDB/repo/10.1/ubuntu bionic Release
  404  Not Found [IP: 213.32.5.7 80]
Hit:6 http://security.ubuntu.com/ubuntu bionic-security InRelease
Hit:7 http://ppa.launchpad.net/chris-lea/redis-server/ubuntu bionic InRelease
Hit:10 http://ppa.launchpad.net/git-core/ppa/ubuntu bionic InRelease
Hit:11 http://ppa.launchpad.net/ondrej/php/ubuntu bionic InRelease
Hit:8 https://downloads.mariadb.com/MariaDB/mariadb-10.3/repo/ubuntu bionic InRelease
Hit:12 http://ppa.launchpad.net/wordops/nginx-wo/ubuntu bionic InRelease
Hit:9 https://downloads.mariadb.com/Tools/ubuntu bionic InRelease
Reading package lists... Done
**E: The repository 'http://mariadb.mirrors.ovh.net/MariaDB/repo/10.1/ubuntu bionic Release' no longer has a Release file.**
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.

UPDATED NOTE: It looks like the issue is related to the mariadb repository. That it's no longer valid.

I did this command, sudo apt-get upgrade, which seemed to be fine.

After that I tried wo stack upgrade again, with following output:

WordOps dashboard is not installed
Composer isn't installed
Your sites may be down for few seconds if you are upgrading Nginx, PHP-FPM, MariaDB or Redis
Do you want to continue:[y/N]n
Not starting package update

I then did wo clean --all (which was fine), and then sudo apt-get dist-upgrade, as per the instructions found here.

That also seemed to work fine.

After that I tried wo maintenance again, but again it failed:

updating apt-cache, please wait...
Whoops, something went wrong...
Check the WordOps log for more details `tail /var/log/wo/wordops.log` and please try again...

Log content:

2023-08-16 03:45:00,596 (INFO) wo : Cleaning opcache
2023-08-16 03:45:01,581 (INFO) wo : Cleaning Redis cache
2023-08-16 03:45:01,581 (DEBUG) wo.core.logging : Running command: redis-cli flushall
2023-08-16 03:45:01,661 (DEBUG) wo.core.logging : Command Output: OK
,
Command Error:
2023-08-16 03:49:29,473 (INFO) wo : Initializing WordOps Database
2023-08-16 03:49:29,477 (INFO) wo : updating apt-cache, please wait...
2023-08-16 03:49:35,889 (INFO) wo : Whoops, something went wrong...
2023-08-16 03:49:35,890 (ERROR) wo : Check the WordOps log for more details `tail /var/log/wo/wordops.log` and please try again...

The distribution info is:

Distributor ID: Ubuntu
Description:    Ubuntu 18.04.6 LTS
Release:        18.04
Codename:       bionic

~~At this point I have no idea what the issue is, nor what else I can try to resolve it.~~

See update in my reply ...