diff --git a/addons/web_editor/models/assets.py b/addons/web_editor/models/assets.py
index 4c304416dd8..4fcc5974893 100644
--- a/addons/web_editor/models/assets.py
+++ b/addons/web_editor/models/assets.py
@@ -71,8 +71,8 @@ class Assets(models.AbstractModel):
                 'mimetype': (file_type == 'js' and 'text/javascript' or 'text/scss'),
                 'datas': datas,
                 'url': custom_url,
+                **self._save_asset_attachment_hook(),
             }
-            new_attach.update(self._save_asset_hook())
             self.env["ir.attachment"].create(new_attach)
 
             # Create an asset with the new attachment
@@ -216,10 +216,21 @@ class Assets(models.AbstractModel):
         return self.env['ir.asset'].search([('path', 'like', url)])
 
     @api.model
-    def _save_asset_hook(self):
+    def _save_asset_attachment_hook(self):
         """
         Returns the additional values to use to write the DB on customized
-        attachment and asset creation.
+        ir.attachment creation.
+
+        Returns:
+            dict
+        """
+        return {}
+
+    @api.model
+    def _save_asset_hook(self):
+        """
+        Returns the additional values to use to write the DB on customized
+        ir.asset creation.
 
         Returns:
             dict
diff --git a/addons/website/__init__.py b/addons/website/__init__.py
index ab49f7f88cf..d0db9014124 100644
--- a/addons/website/__init__.py
+++ b/addons/website/__init__.py
@@ -19,6 +19,14 @@ def uninstall_hook(cr, registry):
     env['ir.asset'].search(website_domain).unlink()
     env['ir.ui.view'].search(website_domain).with_context(active_test=False, _force_unlink=True).unlink()
 
+    # Cleanup records which are related to websites and will not be autocleaned
+    # by the uninstall operation. This must be done here in the uninstall_hook
+    # as during an uninstallation, `unlink` is not called for records which were
+    # created by the user (not XML data). Same goes for @api.ondelete available
+    # from 15.0 and above.
+    env['website'].search([])._remove_attachments_on_website_unlink()
+
+    # Properly unlink website_id from ir.model.fields
     def rem_website_id_null(dbname):
         db_registry = odoo.modules.registry.Registry.new(dbname)
         with db_registry.cursor() as cr:
diff --git a/addons/website/models/assets.py b/addons/website/models/assets.py
index de62ddcb83b..c4793ae1b7a 100644
--- a/addons/website/models/assets.py
+++ b/addons/website/models/assets.py
@@ -143,7 +143,13 @@ class Assets(models.AbstractModel):
             self = self.sudo()
         website = self.env['website'].get_current_website()
         res = super()._get_custom_attachment(custom_url, op=op)
-        return res.with_context(website_id=website.id).filtered(lambda x: not x.website_id or x.website_id == website)
+        # See _save_asset_attachment_hook -> it is guaranteed that the
+        # attachment we are looking for has a website_id. When we serve an
+        # attachment we normally serve the ones which have the right website_id
+        # or no website_id at all (which means "available to all websites", of
+        # course if they are marked "public"). But this does not apply in this
+        # case of customized asset files.
+        return res.with_context(website_id=website.id).filtered(lambda x: x.website_id == website)
 
     @api.model
     def _get_custom_asset(self, custom_url):
@@ -159,15 +165,24 @@ class Assets(models.AbstractModel):
         res = super()._get_custom_asset(custom_url)
         return res.with_context(website_id=website.id).filter_duplicate()
 
+    @api.model
+    def _add_website_id(self, values):
+        website = self.env['website'].get_current_website()
+        values['website_id'] = website.id
+        return values
+
+    @api.model
+    def _save_asset_attachment_hook(self):
+        """
+        See web_editor.Assets._save_asset_attachment_hook
+        Extend to add website ID at ir.attachment creation.
+        """
+        return self._add_website_id(super()._save_asset_attachment_hook())
+
     @api.model
     def _save_asset_hook(self):
         """
         See web_editor.Assets._save_asset_hook
-        Extend to add website ID at attachment creation.
+        Extend to add website ID at ir.asset creation.
         """
-        res = super()._save_asset_hook()
-
-        website = self.env['website'].get_current_website()
-        if website:
-            res['website_id'] = website.id
-        return res
+        return self._add_website_id(super()._save_asset_hook())
diff --git a/addons/website/models/website.py b/addons/website/models/website.py
index d7c95485282..48214aa0814 100644
--- a/addons/website/models/website.py
+++ b/addons/website/models/website.py
@@ -288,6 +288,14 @@ class Website(models.Model):
             raise UserError(_('You must keep at least one website.'))
 
     def unlink(self):
+        self._remove_attachments_on_website_unlink()
+
+        companies = self.company_id
+        res = super().unlink()
+        companies._compute_website_id()
+        return res
+
+    def _remove_attachments_on_website_unlink(self):
         # Do not delete invoices, delete what's strictly necessary
         attachments_to_unlink = self.env['ir.attachment'].search([
             ('website_id', 'in', self.ids),
@@ -297,10 +305,6 @@ class Website(models.Model):
             ('url', 'ilike', '.assets\\_'),
         ])
         attachments_to_unlink.unlink()
-        companies = self.company_id
-        res = super(Website, self).unlink()
-        companies._compute_website_id()
-        return res
 
     def create_and_redirect_configurator(self):
         self._force()