When upgrading to Drupal 9 it can be handy to look up the uninstalled modules first, to remove them.
Use this command:
drush pm:list --type=Module --status="disabled,not installed" --no-core
This resulted for me in this list:
--------------------------------- ------------------------------------------------------------------------ ---------- ----------------
Package Name Status Version
--------------------------------- ------------------------------------------------------------------------ ---------- ----------------
Spam control CAPTCHA (captcha) Disabled 8.x-1.2
Spam control Image CAPTCHA (image_captcha) Disabled 8.x-1.2
Testing captcha long form id test module (captcha_long_form_id_test) Disabled 8.x-1.2
Testing Captcha Test (captcha_test) Disabled 8.x-1.2
Chaos tool suite (Experimental) Chaos Tools Blocks (ctools_block) Disabled 8.x-3.7
Other Entity Mask (ctools_entity_mask) Disabled 8.x-3.7
Chaos tool suite (Experimental) Chaos Tools Views (ctools_views) Disabled 8.x-3.7
Web services Default content (default_content) Disabled 8.x-1.0-alpha9
Media Entity Browser IEF (entity_browser_entity_form) Disabled 8.x-2.6
Media Entity Browser example (entity_browser_example) Disabled 8.x-2.6
Search Facets Range Widget (facets_range_widget) Disabled 8.x-1.8
Search Facets summary (Experimental) (facets_summary) Disabled 8.x-1.8
Migration Field Group Migrate (field_group_migrate) Disabled 8.x-3.1
Field types Formatter field (formatter_field) Disabled 8.x-1.1
Paragraphs Paragraphs Demo (paragraphs_demo) Disabled 8.x-1.12
Paragraphs Paragraphs Library (paragraphs_library) Disabled 8.x-1.12
Paragraphs Paragraphs Type Permissions (paragraphs_type_permissions) Disabled 8.x-1.12
Spam control reCAPTCHA (recaptcha) Disabled 8.x-2.5
Other Redirect Domain (redirect_domain) Disabled 8.x-1.6
Search Database Search Defaults (search_api_db_defaults) Disabled 8.x-1.19
Search Search API Sort Priority: Solr Support (search_api_sort_priority_solr) Disabled 8.x-1.9
SEO Simple XML Sitemap (Search engines) (simple_sitemap_engines) Disabled 8.x-3.10
SEO Simple XML Sitemap (Views) (simple_sitemap_views) Disabled 8.x-3.10
Social media Social share (social_share) Disabled 8.x-2.0-beta6
Other Typed Data (typed_data) Disabled 8.x-1.0-alpha5
Video Embed Field Video Embed Media - Migrate to core oEmbed (vem_migrate_oembed) Disabled 8.x-2.4
Video Embed Field Video Embed Media (video_embed_media) Disabled 8.x-2.4
Video Embed Field Video Embed WYSIWYG (video_embed_wysiwyg) Disabled 8.x-2.4
Video Embed Field Video Embed Field (video_embed_field) Disabled 8.x-2.4
Views Bulk Operations Actions Permissions (actions_permissions) Disabled 8.x-3.13
Examples Views Bulk Operations example (views_bulk_operations_example) Disabled 8.x-3.13