I got frustrated with the invoicing landscape being too complex and pricy and have been using a Google Sheet for the last ~10 years. It has an export to PDF button and then I email the PDF to the client. It’s easy enough for any grid-style design which is all you need with an invoice.
What advantages does Invoice Dragon have over a Google Sheet?
I use Python scripts to generate LaTeX invoices/offers/payslips from yaml files. It works very smoothly.
Of course it is more effort than using the built-in templates from the bookkeeping software, but it looks much nicer and I only do a few per month so it is not many minutes wasted.
The effort spent building up these scripts to their current level is perhaps impossible to motivate with any rational arguments... But I had fun doing it!