Yes.
There are a lot of issues going on right now and major violations of the separation of powers and the bill of rights, but having an ash dab on your forehead isn't one of them.
The executive branch gutting agencies set up by congress is illegal. It's up to congress to pass legislation that defunds them, the executive branch is overreaching while the majority party in congress is just letting it happen.
But having an ash dab on your forehead, even if you went out of the way to make it theatrical, is protected under our freedom of religion and freedom of expression. That's not a violation of separation of church and state. Now if Rubio had ordered his staff members to observe Ash Wednesday regardless of their religious affiliation, that would be a violation.
But doing it himself isn't.
Is it a dog whistle to fundamentalists? Maybe. But there's clear illegal activity to be upset about and we should focus outrage on that.
Furthermore, Elon's nazi salute while abhorrent is also covered under freedom of expression. Though we are all free to judge him for his expressions and his speech, and free to refuse to do business with his companies. Was that a dog whistle to extremists? Hell yes it was, but it's still not illegal.
What the Department of Oligarchs Gutting Everything is doing is illegal, it is usurping the power of the purse from congress and congressional Republicans are just letting it happen.