Having experienced the above error and trying all sorts of solutions offered, to no avail, I stumbled across a possible solution. Open a program in IDE, turn Serial plotter on and off, try to upload again. It seemed to have worked for me.

Avrdude: ser_open(): can't set com-state for "\\.\COM5" - Possible solution

t0ny September 13, 2025, 9:53pm 9

And …

Topic		Replies	Views
Avrdude: ser_open(): can't set com-state for "\\.\COM7" Uploading	12	1919	January 17, 2024
Avrdude: ser_open(): can't set com-state for "\\.\COM5" IDE 1.x	22	10145	May 31, 2024
Avrdude: ser_open(): can't set com-state for "\\.\COM5" Failed uploading: uploading error: exit status 1 Uploading	21	16095	September 20, 2024
Avrdude: ser_open(): can't set com-state for "\\.\COM3" Failed uploading: uploading error: exit status 1 IDE 2.x	39	27988	September 22, 2024
Upload error: avrdude: ser_open(): can't set com-state for "\\.\COM17" Uploading	42	217581	May 6, 2021