If I use the File menu of Firefox to Find in Page… Ctrl+F – without using the keyboard shortcut – then a match is found but may be invisible, and Control-G advances to the next match.

In the screenshot below, the matched word is not either of the pink highlights. The match should be visible with a green highlight.

It's weird, but usable.

I began understanding a little of the complexities.

In response to Control-F:

When I first saw that, I assumed that it was debris from a previous search. On closer inspection, the string is:

in:topic-a503d113-b4b7-4765-8862-15b9912e51d7

– with a space at the tail.

So, I can type Nextcloud then key Enter, the resulting page is https://billboard.bsd.cafe/search?term=in%3Atopic-a503d113-b4b7-4765-8862-15b9912e51d7 Nextcloud&in=titles with the word not found.

If I change the search context from In titles (the default) to In posts, then search results comprise this post alone.

I guess, remote content is not indexed.

Also, for NLI (not logged in) users, the word is not found at the Mastodon instance:

https://infosec.exchange/search?q=Nextcloud&type=statuses