GNU's website has a FAQ section where they say what constitutes and what doesn't constitute a 'single combined program'. My current understanding is that, if you use GPL code in a 'single combined program', your whole 'single combined program' MUST be released under the GPL, as they say here. Is this interpretation enforceable in a court of law and reflected in the license, or is this just the way GNU would like you to think about it and you could realistically argue otherwise in court?
When it comes to law, nothing is ever proven until its been decided in a court of law - even if I walked up to someone in broad daylight and shot them dead in front of hundreds of witnesses, I legally wouldn't have committed murder until I was found guilty by a court. Barring extenuating circumstances (insanity etc), it's of course incredibly likely that a court would find me guilty in that case.
The same principle applies to copyright law - while anybody, the FSF or otherwise, can opine on matters of copyright law, nobody has actually committed a copyright offence unless a court finds that, and every situation is to some extent unique. The FSF's opinion is probably pretty close to what courts in most of the "western world" would rule, but that doesn't mean it's universally true. (I don't know enough about e.g. the Chinese legal system to know how things would potentially go down there).
One thing to note:
I violate my own GPL license
The GPL FAQ is not part of the GPL, therefore it is not something that a GPL licensed program is relying on. The FAQ is the opinion of the FSF, but it is not necessarily the opinion of the author(s) of the software (the ones granting the licence) nor a court. Courts have varying rules about cases setting precedence and those vary from one jurisdiction to another. In many jurisdictions the FSF would have no standing to partake in a lawsuit between the authors and a licensee of the software.
In the specific case of the GPL, one contention is the definition of 'linking'. In Unix, there's a commonly-understood way things are done. But consider a retrocomputer where third-party software can be provided on ROM chips or cartridges - there are no files, no linker tool, just lumps of binary code. Plug in a utility ROM chip and call its functions from your code by their (known) address. In Unix that may be called 'static linking' which is widely considered to cause the ROM to come under the GPL, but those computers operated in a very different way from Unix.
Ultimately, such questions would need to be decided by a court and, to my knowledge, nobody has tested them.
Philip Kendall is technically correct, but here's some more practical not-technically-legal-advice-that-might-technically-be-wrong-in-court from a legal layman such as myself.
In practical terms, the GPL restricts releases of software that links to (statically or dynamically) the GPL-licensed library or program and dictates that those releases must be released under the same license as the library. Or at least this is the commonly understood interpretation and what is written in the FAQ.
The LGPL is essentially the same, but it allows dynamic linking without having to license the program using the dynamically linked library with the same license. (or if you want to get pedantic, it means that end users must be able to swap out the library for their own personal use, which could allow static linking if the user is able to re-compile the program to swap out the library for a different or modified version of that library)
There are some weird edge cases, like how running a commercial set-top-box on Linux is ok even though the Linux kernel is licensed with GPLv2 and it is not generally feasible to jailbreak the box to upgrade or modify the kernel. I'm not entirely sure why this is the case, but there's probably some case law on the matter or something like that.
As to what would qualify as a release, anything that is publicly available for download in any way would probably count as a release for the purposes of the license. If the software is only on your local computer, private repositories, and cloud services that only you (or your company) have access to, then it would not count as a release (most likely) and would not need to comply with the license, even if they were part of a publicly accessible server.
The AGPL and SSPL and some similar licenses try to restrict the use of the software even in servers and managed services. Businesses that license their software in this way (e.g. Redis, MongoDB) are essentially trying to funnel people who don't want to stand up and manage their own clusters toward their premium enterprise services.
Copyleft licenses like the GPL tend to be pretty infectious, so corporate legal counsels will typically advise against using GPL software in your code, if not outright banning it.
Your own personal editor setup and configuration is not a release and I highly doubt it's their intent to prevent end users from customizing their software. You are perfectly within practical limits of the license. Going after you for tinkering with your NeoVim setup would conflict with the entire GNU Free Software philosophy, so they wouldn't sue even if they technically could.
Almost all limitations of copyleft licenses only practically apply to commercial use or when combining multiple open-source projects that are licensed incompatibly.