I am so glad I'm not the only one who is finding this puzzle absolutely impossible today. I've even had to resort to using one of those solver things where you type in the letters you have with ? for the ones you haven't and it comes up with a selection of answers. Hate doing it but...
Anyway, I'm stuck on:
26a: The aged are welcomed into German band (6)
g?r?e?
18d: sauce added principally into Italian food? p?s?a?a
I thought maybe passata but something seems out of place.
23d. At the outset, straining posterior muscle produces an amusing noise (5). s???t
25a: White lie, mostly tall story ultimately. (4) ??l?
Thanks!