Problem ID to exclude specific posts from category

Try this:

function exclude_single_posts_cat($query) {
    if ( is_admin() || ! $query->is_main_query() )
        return;
    if ( $query->is_archive() ) {
        $query->set('post__not_in', array('1','2','3'));
    }
}
add_action('pre_get_posts', 'exclude_single_posts_cat');

Issue: The issue in your first approach is you have added extra curly brackets and comma.

Related Posts:

  1. Sticky Posts exceed posts per page limit
  2. Theres a way to use $query->set(‘tax_query’ in pre_get_posts filter?
  3. Modify Taxonomy pages to exclude items in child taxonomies
  4. Obliterate the main query and replace it
  5. Post injection – how to exclude the original post
  6. Adding meta_key via pre_get_posts causes navigation to disappear
  7. Sorting posts that has a meta value first then the rest of the posts
  8. pre_get_posts on a page
  9. How pre_get_posts filter by roles in WP Admin
  10. Weird problem with pre_get_posts and $query->is_page()
  11. Why is ‘pre_get_posts’ having no effect?
  12. Date Query to Pull Current and Future Posts
  13. pre_get_posts all posts and custom post type with certain tag
  14. Using Sessions to Filter Posts – bad thing?
  15. pre_get_posts and the blog page
  16. Archive by custom post type and custom date field
  17. pre_get_post filter returns results when there should not be
  18. Trying to exclude first 5 posts from the first page on the homepage
  19. Exclude a WordPress post from pre_get_posts if a field is null
  20. Why the ‘date_query’ is not working in ‘pre_get_posts’ hook?
  21. Only show certain post types in recent posts widget
  22. pre_get_posts for exclude category
  23. pre_get_posts: using tax_query only for certain post type
  24. pre_get_posts dont firing… Anybody knows whats the wrong with my code?
  25. Restrict Search Query To After Specific Date
  26. WP_Error not displaying errors
  27. Show all posts even if URL points to a single one
  28. How to achieve post_status__not_in?
  29. Ordering by meta_key
  30. Using a pre_get_posts filter to search for multiple strings on all meta values
  31. Removing taxonomy query by pre_get_posts
  32. Using different parameters for different queries with pre get posts in functions.php
  33. how to restrict posts_request filter to the main query only
  34. Automatically applying a pre_get_posts filter for child categories only
  35. How to override a query and display specific page by ID?
  36. pre_get_posts variables
  37. Another query in pre_get_post cause memory issue
  38. pre_get_posts having no effect on my category archive
  39. pre_get_posts returns non property object when using posts__not_in
  40. Override tax_query with pre_get_posts to include other term_ids on a single category
  41. $query->is_main_query() is causing query’s tax_query to be ignored
  42. Menu disappears when meta_key changed [closed]
  43. pre_get_posts with multiple queries
  44. How to show the last and newest modified post in a custom category?
  45. Altering the main query using get_post_meta() in pre_get_posts
  46. Why query by specific date with variables doesn’t return same result that with harcoded integers?
  47. Sort WordPress Archive by multiple oderby arguments in pre_get_posts action
  48. Exclude post type with pre_get_posts?
  49. Exclude page by title for non admins
  50. problem with setting tax_query in pre_get_posts
  51. Modify Taxonomy pages to exclude items in child taxonomies
  52. Modify author archive query to combine two queries
  53. Change post order on archive to be displayed by most commented being ignored by theme
  54. Complex query using pre_get_posts
  55. Super confusing ‘pre_get_posts’ behavior with $query->set
  56. Having trouble with settings terms as array in pre_get_posts
  57. Override main query for page template
  58. Querying custom taxonomy on category-specific page is overwritten by function
  59. how to get content from other site and show it?
  60. Insert a variable in pre_get_posts
  61. Extend taxonomy term page with other posts
  62. Set a custom number of posts on the first page
  63. Why does this query not SELECT post IDs like a normal query would?
  64. Please ensure me that I’m not crazy using the pre_get_posts [closed]
  65. How to pass >= condition filter to my year custom tax_query
  66. What is the proper way to use pre_get_post?
  67. pre_get_posts has php notice when not on CPT archive
  68. Duplicating event posts in wordpress
  69. Using pre_get_posts to rewrite search query to display posts from multiple taxonomies
  70. WordPress Number of Posts Not Changing With posts_per_page
  71. Show only posts which can be commented
  72. How do I edit pre_get_post for the category the user is currently in?
  73. How to sort posts in admin by titles with dd.mm.yyyy format?
  74. Building an Advanced Search (text, tags, category, custom fields) – Getting the wrong SQL query
  75. Category archive page – loop through posts of certain tag (with pagination) – pre_get_posts
  76. Two loops by pre_get_post on same page
  77. Including only current user’s posts in search
  78. How to sort custom post type posts in default order by multiple fields?
  79. Show Sticky Post at the top but do not show again in the loop?
  80. hide custom post types with specific meta key ON admin backend
  81. Woocommerce: Complex query in pre_get_posts [closed]
  82. pre_get_posts – Trying to get property of non-object warning
  83. pre_get_posts : only get posts by wp_usermeta value
  84. Compare meta key to current date in pre get post
  85. Multiple meta_key ordering with pre_get_posts
  86. pre_get_posts works in post type archive but not in single post
  87. How to apply pre_get_posts to a custom query?
  88. Excluding posts from search results page with meta query not working
  89. pre_user_query vs pre_get_posts
  90. Can I alter the main loop to ‘orderby’ a custom callback?
  91. How to exclude woocommerece product category in search results?
  92. How to show only specific category post by user role without plugin and restrict all other cats
  93. Apply pre_get_posts filter in a certain moment (just for a particular block of posts)
  94. Change post category within pre_get_posts
  95. CPT year wise archive based on custom date Field
  96. WP search in metadata post
  97. Fetch post meta in the same query as the main loop
  98. Filter WP_Query output before it is accessed (pre_get_posts)?
  99. Pre_Get_Posts order DESC not registering
  100. Custom taxonomy with custom meta value is not sorting correctly (query returns the same value for orderby regardless of sort column click)