For invoicing, I made an orgmode template... semi-automated, but my invoice looks good and is correct (VAT / tax calculations etc.) :)

I can't share mine yet, but others have helpfully published theirs https://github.com/woofers/org-invoice-template

And TIL: someone appears to have vibe-coded a mode for invoicing: https://github.com/emacsmirror/org-invox If the code looks okay, I might give it a spin.