Problem found and SOLVED. QuickBooks Desktop For Mac 2019 (latest version, fully updated downloaded directly from Intuit) was apparently choking on the sheer number of Memorized Transactions attempting to remind me to post on January 1st! Even though in preferences I had the "Show Reminders List When QuickBooks Starts" deselected.
SOLUTION: Reset system clock on my Mac (macOS Sonoma) and on my MacBook (macOS Ventura) to December 30, 2023. Company file opened right away on both machines, no problem; home page displayed and Memorized Transaction List open. So, I set all memorized transaactions to "Remind Me" and not to "Automatically Enter", backed up company file and closed file and quit QuickBooks. Reset my computer clocks to set automatically; rebooted both machines; opened my company file on both machines without a problem.
