I use invoice plane every day and I’m a big fan.
However, things have become broken on PHP version 7.4 and above.
Especially notable are the errors when trying to generate a PDF.
I am really hoping there is an update coming as many of us are going to be stuck very soon, if not already. 
This community sadly wants and requests a lot but does not contribute. Beside that we (InvoicePlane) are a very common target of hackers/attackers and have to put in a lot of work to keep the system running.
On top of this I (Martin Hotmann) am just the system maintainer/sponsor, so I basically just host this forum and released two updates some time ago, but my main task here is hosting this forum and the sites - wich I don’t know how long I will still do this.
@Justin check out the PR regarding PHP8: PHP8.1 compatibility by vtq221 · Pull Request #831 · InvoicePlane/InvoicePlane · GitHub
Of course with “things are broken”, there’s nothing to check how it’s broken, etc.
What you need to do is to prepare a bug report.
What are space / traffic platform requirements for new maint if you are looking for somebody else to take over this responsibility from you ?