PlantUML
Install the package.
(with-eval-after-load 'package
(add-to-list 'package-selected-packages 'plantuml-mode))
Use the local PlantUML installation, instead of contacting plantuml.com.
(with-eval-after-load 'plantuml-mode
(setopt plantuml-default-exec-mode 'executable))
;; (with-eval-after-load 'ob-plantuml
;; (setopt org-plantuml-exec-mode 'plantuml))