Thanks for asking the question. My answers are below.
Jenkins may still work on existing installations of Red Hat Enterprise Linux 7 and its derivatives after 16 Nov 2023. I’ve seen no change that will cause existing installations to stop working after 16 Nov 2023. I’d be surprised if such a change were introduced, since there is little benefit to that type of change.
Jenkins developers are not expected to accept patches after 16 Nov 2023 that are specific to fixing issues on Red Hat Enterprise Linux 7 or its derivatives. The Linux support policy describes unsupported platforms by saying:
We do not support the listed platforms and we do not accept patches.
Jenkins 2.414.3, releasing 18 Oct 2023, will be the last Jenkins long term support release to support Red Hat Enterprise Linux 7 and its derivatives. The next Jenkins LTS (baseline undecided, but something like 2.426.1) will release 16 Nov 2023 and will not support Red Hat Enterprise Linux 7 or any of its derivatives.
Jenkins project testing of Red Hat Enterprise Linux 7 and its derivatives will stop on or before 16 Nov 2023. Jenkins plugins like the ssh agents plugin and the git plugin will be free to remove the code they contain that supports the old software versions included in Red Hat Enterprise Linux 7 and its derivatives.
As a maintainer of the git plugin, after 16 Nov 2023 I intend to act as though command line git 1.8 and OpenSSH 7.4 (both included in RHEL 7) no longer exist. I’ll allow myself to make changes that rely on newer versions of command line git (like 2.11 and later) and newer versions of OpenSSH (like 7.8 and later). Some of those changes make break new releases of the git plugin on RHEL 7. If releases of the git plugin after 16 Nov 2023 are broken on RHEL 7, I don’t plan to fix those issues.
Other plugin maintainers and maintainers of Jenkins core are free to release similar changes after 16 Nov 2023. If a change released after 16 Nov 2023 breaks Jenkins core or a plugin on RHEL 7 and does not break on any other platform, that won’t be considered an issue.
The Jenkins LTS release 16 Nov 2023 will not support Red Hat Enterprise Linux 7 or its derivatives. The baseline for that LTS release has not yet been selected, but it will be something like 2.426.1.
You can choose to remain on Jenkins LTS 2.414.3 (scheduled for release on 18 Oct 2023) or on the last weekly version to support RHEL 7.
The Jenkins security team provides security fixes for the most recent Jenkins LTS release and the most recent Jenkins weekly release. Locking yourself to an outdated Jenkins LTS or weekly version is unhealthy because you won’t receive any further security fixes for Jenkins core.