I think a short list would be for 1x GRX from Claris:
Shifters
Calipers (might as well go hydro)
Cassette (get a 11-34 and it should fit)
1x front chainring
Bar tape
Chain
RD
I think it's only worth it if you find the process of piecing things together fun. You also could buy it with Claris, ride it 2000 miles then upgrade so you at least get some wear out of the existing parts.