Ho dimenticato di riportarvi che l'installazione effettuata è della versione 3.10.1+ di Moodle, su un Ubuntu Server 20.04...
Ri: Sito non accessibile dopo installazione tema
Numero di risposte: 1Ri: Sito non accessibile dopo installazione tema
Questa è la schermata che mi viene fuori...

E per ulteriore informazione, abilitando la modalità di Debug attraverso il file config.php, sotto il messaggio di errore, di cui sopra, mi viene riportato quanto segue:
Debug info: theme_boost/header
Error code: filenotfound
Stack trace:
line 123 of /lib/classes/output/mustache_template_finder.php: moodle_exception thrown
line 54 of /lib/classes/output/mustache_filesystem_loader.php: call to core\output\mustache_template_finder::get_template_filepath()
line 99 of /lib/mustache/src/Mustache/Loader/FilesystemLoader.php: call to core\output\mustache_filesystem_loader->getFileName()
line 82 of /lib/mustache/src/Mustache/Loader/FilesystemLoader.php: call to Mustache_Loader_FilesystemLoader->loadFile()
line 681 of /lib/mustache/src/Mustache/Engine.php: call to Mustache_Loader_FilesystemLoader->load()
line 62 of /var/moodledata/localcache/mustache/1614610048/boost_campus/__Mustache_1224c3cfa9baf75bb41da03c680e6f11.php: call to Mustache_Engine->loadPartial()
line 67 of /lib/mustache/src/Mustache/Template.php: call to __Mustache_1224c3cfa9baf75bb41da03c680e6f11->renderInternal()
line 195 of /lib/outputrenderers.php: call to Mustache_Template->render()
line 101 of /theme/boost_campus/layout/columns2.php: call to renderer_base->render_from_template()
line 1374 of /lib/outputrenderers.php: call to include()
line 1304 of /lib/outputrenderers.php: call to core_renderer->render_page_layout()
line 165 of /my/index.php: call to core_renderer->header()
Debug info: theme_boost/header
Error code: filenotfound
Stack trace:
line 123 of /lib/classes/output/mustache_template_finder.php: moodle_exception thrown
line 54 of /lib/classes/output/mustache_filesystem_loader.php: call to core\output\mustache_template_finder::get_template_filepath()
line 99 of /lib/mustache/src/Mustache/Loader/FilesystemLoader.php: call to core\output\mustache_filesystem_loader->getFileName()
line 82 of /lib/mustache/src/Mustache/Loader/FilesystemLoader.php: call to Mustache_Loader_FilesystemLoader->loadFile()
line 681 of /lib/mustache/src/Mustache/Engine.php: call to Mustache_Loader_FilesystemLoader->load()
line 62 of /var/moodledata/localcache/mustache/1614610048/boost_campus/__Mustache_1224c3cfa9baf75bb41da03c680e6f11.php: call to Mustache_Engine->loadPartial()
line 67 of /lib/mustache/src/Mustache/Template.php: call to __Mustache_1224c3cfa9baf75bb41da03c680e6f11->renderInternal()
line 195 of /lib/outputrenderers.php: call to Mustache_Template->render()
line 101 of /theme/boost_campus/layout/columns2.php: call to renderer_base->render_from_template()
line 1374 of /lib/outputrenderers.php: call to include()
line 1304 of /lib/outputrenderers.php: call to core_renderer->render_page_layout()
line 165 of /my/index.php: call to core_renderer->header()