I was similarly in this position and came up with an easy solution. I switched to H&R Block software this year. The H&R Block equivalent of TurboTax Deluxe software was half the price too. H&R Block installed, imported my previous year's TurboTax file, and ran just fine. So it's clear this is a TurboTax issue.
I have an older mac which runs just fine for everything I use it for, it just cannot be be upgraded past Max OS X 10.13.6 TurboTax online would have cost me even more since it's a separate fee per person, not being inclusive of a few people's taxes like the software is.
