It seems I'm not the only one experiencing STS update problems:
Spring Tool Suite 4 Version: 4.18.1.RELEASE Build Id: 202305021758
Updates are impossible given the original update sites:
| Item | Location |
|---|---|
| Latest Eclipse Release | https://download.eclipse.org/releases/latest |
| Linux Tools Docker Tooling | https://download.eclipse.org/linuxtools/update-docker |
| Spring Tool Suite 4 | https://download.springsource.com/release/TOOLS/sts4/update/latest |
| Spring Tools 4 Language Servers for Eclipse | https://download.springsource.com/release/TOOLS/sts4-language-server-integrations |
!SUBENTRY 3 org.eclipse.equinox.p2.director 4 0 2023-12-16 10:40:40.616 !MESSAGE From: Eclipse Platform 4.27.0.v20230302-0300 (org.eclipse.platform.feature.group 4.27.0.v20230302-0300) !SUBENTRY 3 org.eclipse.equinox.p2.director 4 0 2023-12-16 10:40:40.616 !MESSAGE To: org.eclipse.equinox.p2.iu; org.eclipse.compare [3.8.500.v20220812-1406,3.8.500.v20220812-1406] !SUBENTRY 2 org.eclipse.equinox.p2.director 4 1 2023-12-16 10:40:40.616 !MESSAGE Cannot satisfy dependency: !SUBENTRY 3 org.eclipse.equinox.p2.director 4 0 2023-12-16 10:40:40.616 !MESSAGE From: Spring Tool Suite 4 4.18.1.202305021758 (org.springframework.boot.ide.branding.sts4 4.18.1.202305021758) !SUBENTRY 3 org.eclipse.equinox.p2.director 4 0 2023-12-16 10:40:40.616 !MESSAGE To: org.eclipse.equinox.p2.iu; org.eclipse.platform.feature.group [4.27.0.v20230302-0300,4.27.0.v20230302-0300]
!ENTRY org.eclipse.equinox.p2.engine 4 4 2023-12-16 10:50:25.802 !MESSAGE An error occurred while collecting items to be installed !SUBENTRY 1 org.eclipse.equinox.p2.engine 4 0 2023-12-16 10:50:25.802 !MESSAGE session context was:(profile=DefaultProfile, phase=org.eclipse.equinox.internal.p2.engine.phases.Collect, operand=, action=). !SUBENTRY 1 org.eclipse.equinox.p2.artifact.repository 4 0 2023-12-16 10:50:25.802 !MESSAGE No repository found containing: osgi.bundle,bcpg,1.76.0 !SUBENTRY 1 org.eclipse.equinox.p2.artifact.repository 4 0 2023-12-16 10:50:25.802 !MESSAGE No repository found containing: osgi.bundle,bcprov,1.76.0 !SUBENTRY 1 org.eclipse.equinox.p2.artifact.repository 4 0 2023-12-16 10:50:25.802 !MESSAGE No repository found containing: osgi.bundle,com.fasterxml.jackson.core.jackson-annotations,2.15.2 !SUBENTRY 1 org.eclipse.equinox.p2.artifact.repository 4 0 2023-12-16 10:50:25.802 !MESSAGE No repository found containing: osgi.bundle,com.fasterxml.jackson.core.jackson-core,2.15.2 !SUBENTRY 1 org.eclipse.equinox.p2.artifact.repository 4 0 2023-12-16 10:50:25.802 !MESSAGE No repository found containing: osgi.bundle,com.fasterxml.jackson.core.jackson-databind,2.15.2
...error log goes on for miles
Turns out there is nothing wrong with the update sites. I just did not understand the update process.
I had run across some comments about issues with 'cache'.
The solution was simply to "Reload" the update sites.
See Martin Lippert's answer and first solution here:
Spring Tool Suite4 Update Failed, Error Showing