Would it be an option to make a simple REST-API call and beautify the output with some sort of editor?
probably this provides a better formatted output (by pagination):
Might all not be pretty and needs polishing what you get back from API - but presumably a bit faster than copying 20 lines per page, am I missing something obvious by this suggestion?
That does answer the question of "do you want a list of fields or the issue data", unlike "I want to dump out all the customfields"
There is no list of custom field export function in Jira, most of us simply scrape it out of the admin screen. It's not often people want a list like that though, it's only really of use when you're starting some tidying up or doing migration and merges. When doing migrations and merges though, we tend to use tools like Configuration Manager or Project Configurator - these can list all the fields in a single place.
Trying to dump to Excel the list of 800 - 1000 custom fields seems like a task in the admin screen when you only show 20 per screen. Not sure I want to waste my time there. Can you point me where to access the tools Configuration Manager or Project Configurator in the cloud version that you are referencing? Thanks.
You're right, 20 lines at a time really is a pain in the neck
Configuration Manager and Project Configurator are both marketplace apps, there are some others that help with migrations, but I'm not sure if they'll drop out a list of fields. I should also be explicit - I work for the company that turns out of of them.
You might also want to check out Optimiser for Jira - it has a section on custom fields that might be more helpful than a flat list.