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?
Fairphone 5 has 5 year warranty. Sure that’s not 4, but the title makes it seem that 4 is longest out there.
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.
I have had basically no issues with my setup: Edgerouter 4 (overkill, had a lower end Edgerouter earlier with no issues except the power adapter died, other hardware was fine). Some pretty basic unifi AP. As well as some cheap dumb gigabit switches. Can basically fire and forget them. Relatively easy to do most things I need on it. Never needed a reboot outside of upgrades. No stability issues, unlike basically all other home grade all in one stuff I have experienced in the past.
I have been satisfied with beancount. https://github.com/beancount/beancount and fava as a ui. It’s text based so it is easy to automate imports and exports. It can seem daunting at first to create importers in Python, but it’s pretty basic scripting.
Text based accounting lends itself well to easy experimentation with version control.
I tried gnucash for a while, but it felt so slow and not flexible enough for me.