It is a nice flannel from Portuguese Flannel via No Man Walks Alone.
Since it was from last fall, looks like it is no longer available, but they have a similar shirt here:
https://nomanwalksalone.com//rude-shirt-in-blue-donegal-cotton-hopsack-restock.html
And End has similar here:
https://www.endclothing.com/us/portuguese-flannel-teca-shirt-pf-tcfs-nv.html
I need my eyes (or computer screen) checked...I thought for sure that was grey flannel in the pic I posted. I liked that it looked (to me) like an approximation of mid-grey flannel trousers.