What kind of anstrengend?

Yes, you can say a tough day, if you mean it was difficult, hard to endure, and it didn't end happily. A tough day is basically a bad day for you, one you don't like to think about. Maybe you would even rather it had not happened, wish you hadn't had to go through it. Not always, but often, 'tough' suggests some emotional difficulty, something that made you feel sad or discouraged.

A day can also be busy, long, tiring, stressful, etc. without necessarily being as bad as tough, especially if at the end you feel it was worth the effort or there was a good result in the end. It's not an absolute distinction, but to me there are other things that are more common if your meaning is a little less negative.

Hängt von der Art der Anstregung ab - 'tough' hat hier auch was von schwierig. Wenn es einfach nur viel Arbeit war, würde ich es nicht nehmen, dann lieber hard oder exhausting oder so was.

Ich meinte anstrengend von der Arbeit, aber nicht nur körperlich , sondern auch vom Kopf her.

Dann passt alles, was hm im letzen Absatz vorschlägt, aber nicht 'tough'.

I would consider 'tough' fine for this context.
It also depends how it's expressed.

AE

(Maybe strenuous.)