如果你正在写一个条件语句里面的文件，你需要直接告诉它打印。

if (RMCAv_Graph == T){
   Save_Path = file.path(Sub_Folder_Path, "RMCAv.tiff")
   tiff(file = Save_Path, units = "in", width = 5, height = 5, res = 600)
   RMCAv_Plot %>% print()
   dev.off()
}

或不带管道：

if (RMCAv_Graph == T){
   Save_Path = file.path(Sub_Folder_Path, "RMCAv.tiff")
   tiff(file = Save_Path, units = "in", width = 5, height = 5, res = 600)
   print(RMCAv_Plot)
   dev.off()
}