This response is coming very late but I will leave a comment here incase anyone else comes across this issue in the future.

Below is how to run the "Sitemap SEO Generation Job" under a different user (so you can deactivate the current user its being run as)

1. Navigate to setup, then scheduled job and hit 'Delete' next to the  "Sitemap SEO Generation Job" you want to reschedule.

2. Login as the user you would like to replace the original user, then navigate to 'All Sites', got to 'Builder' and publish the site.

3. After publishing the site, a new "Sitemap SEO Generation Job" will appear on the scheduled jobs under the name of the user who published the site.

4. You can now proceed to deactivate the previous user.

Refer to this feed to see a similar answer regarding this:

https://trailhead.salesforce.com/trailblazer-community/feed/0D54S00000BtlG7SAJ

Thanks!