Here is the specific section of the kodi.log that shows what is happening:
2023-07-05 21:23:00.818 T:139783248335744 NOTICE: Starting Kodi from Debian (18.6 Debian package version: 2:18.6+dfsg1-2ubuntu1). Platform: Linux x86 64-bit
2023-07-05 21:23:00.818 T:139783248335744 NOTICE: Using Release Kodi from Debian x64 build
2023-07-05 21:23:00.818 T:139783248335744 NOTICE: Kodi from Debian compiled 2020-04-03 by GCC 9.3.0 for Linux x86 64-bit version 5.4.27 (328731)
2023-07-05 21:23:00.818 T:139783248335744 NOTICE: Running on Ubuntu 20.04.6 LTS, kernel: Linux x86 64-bit version 5.4.0-153-generic
... snip ...
2023-07-05 21:26:34.030 T:139925619861248 NOTICE: VideoInfoScanner: Starting scan ..
2023-07-05 21:26:34.031 T:139925619861248 DEBUG: CAddonSettings[metadata.themoviedb.org]: loading setting definitions
2023-07-05 21:26:34.031 T:139925619861248 DEBUG: CAddonSettings[metadata.themoviedb.org]: trying to load setting definitions from old format...
2023-07-05 21:26:34.031 T:139925619861248 DEBUG: CAddonSettings[metadata.themoviedb.org]: loading setting values
2023-07-05 21:26:34.032 T:139925619861248 DEBUG: VideoInfoScanner: Scanning dir '/home/nnn/Videos/Film/Monkeybone (2001)/' as not in the database
2023-07-05 21:26:34.032 T:139925619861248 DEBUG: CAddonSettings[metadata.themoviedb.org]: loading setting definitions
2023-07-05 21:26:34.032 T:139925619861248 DEBUG: CAddonSettings[metadata.themoviedb.org]: trying to load setting definitions from old format...
2023-07-05 21:26:34.032 T:139925619861248 DEBUG: CAddonSettings[metadata.themoviedb.org]: loading setting values
2023-07-05 21:26:34.033 T:139925619861248 DEBUG: FindMovie: Searching for 'Monkeybone' using The Movie Database scraper (path: '/usr/share/kodi/addons/metadata.themoviedb.org', content: 'movies', version: '5.1.7')
2023-07-05 21:26:34.037 T:139925619861248 DEBUG: scraper: CreateSearchUrl returned <url>https://api.tmdb.org/3/search/movie?api_key=f090bb54758cabf231fb605d3e3e0468&query=Monkeybone&year=2001&language=en</url>
2023-07-05 21:26:34.037 T:139925619861248 DEBUG: CurlFile::Open(0x7f42e82b3170) https://api.tmdb.org/3/search/movie?api_key=f090bb54758cabf231fb605d3e3e0468&query=Monkeybone&year=2001&language=en
2023-07-05 21:26:34.037 T:139925619861248 INFO: easy_acquire - Created session to https://api.tmdb.org
2023-07-05 21:26:34.174 T:139925619861248 DEBUG: Get: Using "UTF-8" charset for "https://api.tmdb.org/3/search/movie?api_key=f090bb54758cabf231fb605d3e3e0468&query=Monkeybone&year=2001&language=en"
2023-07-05 21:26:34.175 T:139925619861248 DEBUG: scraper: GetSearchResults returned <results></results>
2023-07-05 21:26:34.175 T:139925619861248 DEBUG: FindMovie: Searching for 'Monkeybone' using The Movie Database scraper (path: '/usr/share/kodi/addons/metadata.themoviedb.org', content: 'movies', version: '5.1.7')
2023-07-05 21:26:34.175 T:139925619861248 DEBUG: scraper: CreateSearchUrl returned <url>https://api.tmdb.org/3/search/movie?api_key=f090bb54758cabf231fb605d3e3e0468&query=Monkeybone&year=&language=en</url>
2023-07-05 21:26:34.175 T:139925619861248 DEBUG: CurlFile::Open(0x7f42e82b3170) https://api.tmdb.org/3/search/movie?api_key=f090bb54758cabf231fb605d3e3e0468&query=Monkeybone&year=&language=en
2023-07-05 21:26:34.192 T:139925619861248 DEBUG: Get: Using "UTF-8" charset for "https://api.tmdb.org/3/search/movie?api_key=f090bb54758cabf231fb605d3e3e0468&query=Monkeybone&year=&language=en"
2023-07-05 21:26:34.193 T:139925619861248 DEBUG: scraper: GetSearchResults returned <results></results>
2023-07-05 21:26:34.193 T:139925619861248 WARNING: No information found for item '/home/nnn/Videos/Film/Monkeybone (2001)/Monkeybone.2001.1080p.BluRay.x264.DD5.1-FGT.mkv', it won't be added to the library.
2023-07-05 21:26:34.194 T:139925619861248 DEBUG: VideoInfoScanner: No (new) information was found in dir /home/nnn/Videos/Film/Monkeybone (2001)/
2023-07-05 21:26:34.262 T:139925619861248 NOTICE: VideoInfoScanner: Finished scan. Scanning for video info took 00:00
If I go directly to that URL (https://api.tmdb.org/3/search/movie...) I actually get a valid result. But if I go to the XML wrapped url, from this line:
2023-07-05 21:26:34.037 T:139925619861248 DEBUG: scraper: CreateSearchUrl returned <url>https://api.tmdb.org/3/search/movie?api_key=f090bb54758cabf231fb605d3e3e0468&query=Monkeybone&year=2001&language=en</url>
I get an empty result set. This makes sense because of the & -> & encoding that corrupts the query.
This wasn't happening last week. I performed a Ubuntu system update over the weekend, but it would be pretty wild for that to break something like this. Possibly something changed at theMovieDB where encoding damaged URLs used to work but this was "fixed" and now they don't?