As it was already announced last year, Synology has delivered on their promise to remove a good amount of apps from their Package center.
The process was split into two categories. The first one was on Dec 25th, 2019, when category one packages reached end of software maintenance. This means that those apps were still working but no support was given.
Category one (end of support):
PHP 5.6 *
PHP 7.0 *
NOTE: PHP 5.6 and 7 were still supported due to dependacies until stage two (June 30th 2020)
Yesterday, June 30th, category two apps reached the end of life. This means that as of today you will no longer be able to download these apps from the Package center:
Category two (end of life):
Logitech media server
Keep in mind that all of these apps can still be found using the following URL. This will allow you to downlad the SPK files manually and install them using the "Manual install" button inside Package Center.
Personally I would suggest (if possible of course), in case you need any of these apps, to try and run them using Docker platform. As I wrote in my previous articles, Docker support is getting more and more momentum and support, and it is no wonder that Synology will stop supporting 3rd party open source apps as part of their Package Center. Another benefit will be that you will not be threathed by EOL announcement from Synology or any other brand, because you will be able to transfer your Docker containers to a different Docker contianer host without any trouble at all. Finally, being sandboxed outside of DSM and not affected by any system change, you can be sure that all your apps will continue to work.
For example, one app that Synology no longer supports in this list is Mono. It is actually a framework more then an app but the problem here is that a lot of Mono dependent apps will stop working and will not be able to install at all (like Sonarr, Radarr, etc). Now you will be able to get it and install it using a custom repository like synocommunity for example, but even so, I would still suggest Docker solutions for a long term piece of mind.