Best regards informal

https://www.quora.com/Why-is-‘best-regards’-or-‘kind-regards’-considered-to-be-bad-English
https://www.quora.com/What-is-the-difference-between-Regards-Best-regards-Sincerely-Yours-Faithfully-and-all-of-the-other-formulations-Which-one-is-the-best-to-use-in-North-America-in-an-email-conversation
https://english.stackexchange.com/questions/332/which-expressions-can-be-used-to-close-an-email

https://preply.com/en/question/best-regards-vs-warm-regards-41388

https://blog.udemy.com/with-best-regards/