I switched to Twenty Twenty-One, deleted Neve, installed it again and activated it. The header and footer builders are still missing. By the way, I noticed just now that an error_log was generated in the public_html folder:
[25-Aug-2021 01:00:23 UTC] PHP Fatal error: Uncaught Error: Call to a member function get_id() on null in /home/xxxxxxxx/public_html/wp-content/themes/neve/header-footer-grid/templates/component-wrapper.php:13
Stack trace:
#0 /home/xxxxxxxx/public_html/wp-includes/template.php(772): require()
#1 /home/xxxxxxxx/public_html/wp-content/themes/neve/header-footer-grid/Main.php(198): load_template('/home/xxxxxxxx/...', false)
#2 /home/xxxxxxxx/public_html/wp-content/themes/neve/header-footer-grid/Core/Components/Abstract_Component.php(584): HFG\Main->load('component-wrapp...')
#3 /home/xxxxxxxx/public_html/wp-includes/customize/class-wp-customize-partial.php(221): HFG\Core\Components\Abstract_Component->render(Object(WP_Customize_Partial), Array)
#4 /home/xxxxxxxx/public_html/wp-includes/customize/class-wp-customize-selective-refresh.php(371): WP_Customize_Partial->render(Array)
#5 /home/xxxxxxxx/public_html/wp-includes/class-wp-hook.php(303): WP_Customize_Selective_Refresh->handle_render_partials_request('')
#6 /home/xxxxxxxx/public_html/wp-includes/class-w in /home/xxxxxxxx/public_html/wp-content/themes/neve/header-footer-grid/templates/component-wrapper.php on line 13