If there is a fermata in the last bar, ‘tacet al fine’ is apparently not possible. Is there a possibility that Dorico ignores this fermata and shows the “tacet al fine”?
A forum search for “fermata” and “tacet” returned this: https://www.steinberg.net/forums/viewtopic.php?f=246&t=144128&p=777166&hilit=fermata+tacet#p777166
The short answer is “not yet.” If you want, you can create a fermata as a playing technique and assign it only to certain staves.
Thank you, Dan!