Must I have an Office 365 account to use Tiller?

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 It simply becomes outdated, like no XLOOKUP in 2019.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.