XML Parsing Error: not well-formed Line Number 1, Column 1

Hello @zuelius-dtal how are you?

I was testing here and for me worked well, I'll explain what I did on that case; I updated the minifyhtml project to 7.x-1.10 version that was released at January of 2022. I updated the Drupal core for 7.89 and I updated the XML sitemap to 7.x-2.6. After that I cleared all caches, and verify if there is something to update on /update.php or with drush updb. After that you can try again. For me it worked and you works for you as well. If you have any other issues on this process please let us know ok? Thank you so much