I am New and while reading it seems to keep pushing me towards Google Sheets? What is the REAL deal here?

[Mark.S]

Something to keep in mind is that Excel/Office YYYY one-time purchase software isn’t officially supported, since it gets outdated. Microsoft 365 and the free web-based Excel could be used, although I believe 365 is the primary development focus.

Must I have an Office 365 account to use Tiller?

No. I asked the same in this post: You can use the free web browser version of Excel, though. You just need a free Microsoft account. I’ve played with it some and it seems to work with the Tiller Foundation Template, although I haven’t tried linking a bank account and downloading transactions, yet. Like you, I also have a copy of MS Office 2019. It simply becomes outdated, like no XLOOKUP in 2019. I’ve been using Tiller in Google Sheets, since more features are supported there.