I agree with TheDJ that moving consecutive "tr" rows that contain only "th" cells to the "thead" element would work, and wouldn't need any new wikitext syntax. Sortable and the sticky gadget (for wikitable) do this using JavaScript. It should be done for all tables (sortable, wikitable, plain table) so they are easier to style. Ideally, it should be moved during template translation (wikitext to HTML) instead of relying on JavaScript (see No-JavaScript).

I created the Sort under template to reposition the sorting arrows under the text. They can be center or right aligned. I kept the traditional right alignment, which may have some uses. I don't see a need for left alignment, but it can be added if there is a demand.

A discussion has started at Template_talk:Import-blanktable#class=sortunder on adding this functionality to the TemplateStyles, which would use the "sortunder" table class. Below is a version of the styles that might work for this task .

@media screen {
	.client-js .sortunder.sortable:not(.jquery-tablesorter) > * > tr:first-child > th:not(.unsortable),
	.sortunder.jquery-tablesorter th.headerSort {
		background-position: bottom 0.2em right;
		padding-bottom: 1em;
		padding-right: 0.4em;
	}
	.client-js .sortunder.sortable:not(.jquery-tablesorter) > * > tr:first-child > th.unsortable,
	.sortunder.jquery-tablesorter th.unsortable {
		padding-bottom: 1em;
	}
}

@TheDJ Thanks for implementing a fix for iPhones.

I redid the styles for the large COVID-19 tables and added some additional features like a column of left-sticky row headers. Below are the styles and a few tables.

• Template:COVID-19 pandemic data/styles2.css
• Template:2020 monthly cumulative COVID-19 death totals by country
• Template:2021 monthly cumulative COVID-19 death totals by country
• Template:COVID-19 pandemic death rates by country

@Timeshifter
The page you linked to says "This page is obsolete. It is being retained for archival purposes." I'm not really sure where I can set it up.

Just an update on the issues I mentioned above in regards to the work I did. I figured out a fix for the desktop browser issue, which has been implemented.

In T42763#7539855, @Timeshifter wrote:

There are 4 scrolling tables that have long had sticky headers in this section:
*https://en.wikipedia.org/wiki/COVID-19_pandemic_by_country_and_territory#Statistics

Single header rows:
*https://en.wikipedia.org/wiki/Template:COVID-19_vaccination_data
*https://en.wikipedia.org/wiki/Template:Monthly_cumulative_COVID-19_death_totals_by_country_2021

Taller header row:
*https://en.wikipedia.org/wiki/Template:COVID-19_pandemic_death_rates

Template with 2 header rows:
*https://en.wikipedia.org/wiki/Template:Monthly_cumulative_COVID-19_death_totals_by_country

I'm not sure if this helps any, but I've done some work on making table headers sticky while scrolling both on desktop and mobile browsers since Dec 4, 2020. This work is on my sandbox since I'm not familiar with the Wikipedia project/task workflow. Since this is my sandbox, the CSS/JS won't be included for you unless you are logged in as me. The only workaround I can think of is for you to reproduce the CSS and JS files in your sandbox.