Sonic 7 replaces HSSE. Instances might still be named for earlier versions but you should find that Sonic 7 plays/opens in their place.
If the old name bothers you, you can rename the plugin instances by clicking the settings cog for each plugin instance in the Play tab. This is also the same area where you choose expression maps. Simply double click the Plugin Instance name and rename to whatever you like.
Updates to Sonic 7 do NOT uninstall nor replace installations of Sonic SE. The latest versions of Steinberg hosts have no problem with this, and will gracefully ignore HALion Sonic 3 SE and load/use Sonic 7 instead; however, some older hosts, or non-Steinberg hosts can get a bit confused by this (HSSE 3 SE, and Sonic 7 share the same plugin ID, and some hosts just don’t know what to do…might blacklist one or the other…might even crash on plugin scan!).
With this in mind…
If you do not need to run any variant of HALion in a VST2 only host (Such as Sibelius or Finale under Windows) it’s probably best to simply uninstall HALion Sonic SE 3 (HSSE) from your system all together. At this point HALion/Sonic 7 gracefully replaces all previous versions of HALion/Sonic.
I believe this ‘lack of a VST2 plugin’ for Sonic 7 mainly effects Windows users. I’m not positive, but Mac users can probably opt for AU plugins over VST2 in quite a few hosts (and get better support for Native Apple Silicon by doing so).
For Windows users, there are still quite a few mainstream hosts that don’t yet support VST3, and the AU or AAX variants don’t work for them either.
So, if you don’t need VST2…Uninstalling the old HALion Sonic 3 SE is probably the way to go. This is done through your OSes Application manager.
If you DO need to keep a version of HSSE around for the sake of some VST2 only hosts…
I recommend ‘moving’ the VST3 version of Sonic SE to an unscanned directory for safe keeping (can be swapped out with the Sonic 7 one on the extremely rare occasion you might want/need to roll back to HSSE3 for a VST3 host).
On a Windows system move:
“%SYSTEMDRIVE%\Program Files\Common Files\VST3\Steinberg\Sonic SE”
to somewhere that won’t get scanned, such as:
“%SYSTEMDRIVE%\Program Files\Common Files\VST3.disabled\Sonic SE”
This offers a cleaner plugin scan for non-Steinberg hosts that can do VST3. They will simply use Sonic 7 in any projects that were using HSSE before.
You can keep the HALion Sonic SE (HSSE) VST2 plugins in place for hosts that need it. Just be aware that your standalone version of Sonic 3 SE will stop working until such time as you put that Sonic SE plugin back into the system VST3 directory. Other hosts can still scan for and use HSSE3 VST2. While it’s a bad idea unless you have a ‘very specific need’ to force HSSE into play, It’s also possible to pull up the VST2 version of HSSE in Dorico/Cubase/Nuendo (On new Macs you’d probably need Rosetta).
Sonic 7 and HALion 7 no longer come in a VST2 format. Only 64bit VST3, AU, and AAX. So, the only way to use your HALion sounds in VST2 only hosts is through that older HSSE VST2 plugin (or through a VST2>VST3/VST3>VST2 bridge such as the free Kushview, or perhaps something like a registered instance of Bidule. Such products might also get HALion/Sonic 7 working in a VST2 only host as well).
The good news is that if you’ve been using Sonic SE with other hosts that cannot host VST3, AU, or AAX plugins, you’ll still have some means to use the HALion content that came with Dorico in your VST2 only hosts. Those can still find and use the VST2 version of HSSE.