Aller dans le répertoire /home/mastodon/live et appliquer les changements suivants (pour passer à limite à 5000):

diff --git a/app/javascript/mastodon/features/compose/components/compose_form.js b/app/javascript/mastodon/features/compose/components/compose_form.js
index 6a65f44da..b1e364451 100644
--- a/app/javascript/mastodon/features/compose/components/compose_form.js
+++ b/app/javascript/mastodon/features/compose/components/compose_form.js
@@ -90,7 +90,7 @@ class ComposeForm extends ImmutablePureComponent {
     const fulltext = this.getFulltextForCharacterCounting();
     const isOnlyWhitespace = fulltext.length !== 0 && fulltext.trim().length === 0;

-    return !(isSubmitting || isUploading || isChangingUpload || length(fulltext) > 500 || (isOnlyWhitespace && !anyMedia));
+    return !(isSubmitting || isUploading || isChangingUpload || length(fulltext) > 5000 || (isOnlyWhitespace && !anyMedia));
   }

   handleSubmit = (e) => {
@@ -277,7 +277,7 @@ class ComposeForm extends ImmutablePureComponent {
           </div>

           <div className='character-counter__wrapper'>
-            <CharacterCounter max={500} text={this.getFulltextForCharacterCounting()} />
+            <CharacterCounter max={5000} text={this.getFulltextForCharacterCounting()} />
           </div>
         </div>

diff --git a/app/validators/status_length_validator.rb b/app/validators/status_length_validator.rb
index e107912b7..a3cbe5123 100644
--- a/app/validators/status_length_validator.rb
+++ b/app/validators/status_length_validator.rb
@@ -1,7 +1,7 @@
 # frozen_string_literal: true

 class StatusLengthValidator < ActiveModel::Validator
-  MAX_CHARS = 500
+  MAX_CHARS = 5000
   URL_PLACEHOLDER_CHARS = 23
   URL_PLACEHOLDER = 'x' * 23

Puis recompiler les assets

sudo -i -u mastodon
cd live
RAILS_ENV=production bundle exec rails assets:precompile

Enfin redémarrer les services

sudo systemctl restart mastodon-{sidekiq,streaming,web}.service