Sync OPML to Blogroll

Keep your WordPress blogroll in sync with your feed reader.

Instructions

Install, activate, and head over to Settings > Sync OPML to Blogroll to tell WordPress about your OPML endpoint of choice. (E.g., Miniflux’s endpoint usually looks like this: https://your.miniflux.site/v1/export. Other feed readers typically expose OPML documents in a similar manner.)
For a feed to be picked up, it requires both a valid site URL and a valid feed link, though most if not all feed readers will take care of that for you.
Syncs once daily. Importing categories is optional and in a somewhat experimental phase.

Basic Authentication

This plugin supports basic authentication as used by, e.g., Miniflux. Username and password fields may be left blank if not applicable. Note: unless you manually add a SYNC_OPML_BLOGROLL_PASS constant to wp-config.php (see below), your password is saved to WordPress’s database in plaintext format. (That’s basic authentication for you, unfortunately.)
Defining the password in wp-config.php rather than storing it in the database is done by adding the following line to wp-config.php, just before /* That's all, stop editing! Happy publishing. */:

define( 'SYNC_OPML_BLOGROLL_PASS', 'your-password-here' );

If you’ve previously filled out and saved the password field, and only recently added above constant, simply visit Settings > Sync OPML to Blogroll and hit Save Changes to wipe your password from the database.

Front-End Usage

Now, for your links to show up on a page (or in your sidebar, etc.), you’re going to have to add them through either WordPress’s wp_list_bookmarks() function, a shortcode (like the one provided by the Bookmarks Shortcode plugin, or a block (like the Bookmarks block). Or a widget, if your theme supports them.
Like, on one of my sites, which has Bookmarks Shortcode installed, I simply use WordPress’s core Custom HTML block with the exact following content:

<ul id="blogroll">[bookmarks title_li='' categorize=0]</ul>

Yes, the Custom HTML block accepts shortcodes this way. Also, this is but one example.
I know, it seems rather clunky to have to install yet another plugin (or edit your [child] theme’s templates) to actually make this work, and I will provide a built-in alternative in a next version.

Remarks

Link Manager

This plugin explicitly enables the WordPress Link Manager that’s disabled by default since version 3.5. No need for other Link Manager plugins that do the same.

Categories

Importing categories is optional and disabled by default. OPML 2.0 and hierarchical categories are currently not supported. If you find categories are wrongly assigned, you may want to simply disable this option (and, if necessary, define and set categories manually).

Sync Rate

This plugin’ll attempt to fetch and process your OPML once a day. It will also ‘force sync’ immediately after it is first configured or settings are changed. (Not merely saved, but changed.) Syncing is done in the background.
If you somehow need full control of cron actions, you’ll probably want to look into something like WP-Crontrol. (Note: not for novices!)

On “Syncing”

While feeds that are deleted from your reader and thus OPML endpoint will also be deleted from WordPress, existing WordPress bookmarks without a feed link are left alone.
Names, categories and even site URLs can be edited after feeds are imported, and changes will not be overwritten by future sync actions. (That also means that name changes on your feed reader’s end will not affect WordPress links. This plugin, in fact, only looks at feed URLs to determine what to do.)
“Syncing,” by the way, only works in one direction: from your OPML endpoint to your WordPress blogroll.