I'm having a problem with Table to Table in Pro 2.6 also. It's only working for tables - not for Feature Classes, even though Table to Table is the tool that's automatically used when you choose to Export a feature class.
I went to Pro 2.6.1 thinking that might solve the problem but it didn't. I don't have an expression defined in my Table to Table run, but I keep getting 'Error 160912: Failed to evaluate Arcade expression'.
I guess I'll try re-installing to see if that fixes this issue.