I had an issue where one keyboard (worked with another one) worked in bootloader, but not when entering the encryption password after that. I believe I solved that by moving keyboard earlier in the module list in mkinitcpio.conf. Maybe something similar would solve your issue?

You seem to have a lot of recommendations already, but I just wanted to mention beancount as well. It’s a decently powerful plain text accounting software. Not sure if it does invoicing.

For me it has been good because I think it is fun to hack some new functionality together that I feel missing. E.g. parse pdf receipts and break down transactions into postings based on what is in the receipt. But it you aren’t interested in simple Python programming, I’d probably not recommend it.

Being able to easily version control it using git is really helpful when you are trying things.