ggplot will only do what you tell it to do. In your code you've just told it to use Group name as the element of the x axis. If you want it to separate out by another variable, eg Pool, then you need to mention that variable, as it won't guess what's in your mind.
The syntax and options of ggplot2 can be pretty complex imho, however, and it's worth googling or searching Stack Exchange for tips on how others have made it work. Or read Kieran Healy's Data Visualisation book.
Here's a couple of ways to do what I think you're trying to do:
library(dplyr)
library(ggplot2)
ggplot2::midwest %>%
filter(category == "ALR") %>%
ggplot(aes(x = state, y = popdensity, fill = county)) +
geom_col(position = position_dodge2(preserve = "single"))

ggplot2::midwest %>%
filter(category == "ALR") %>%
ggplot(aes(x = county, y = popdensity)) +
geom_col(position = "dodge", fill = "slategrey") +
facet_grid(~state, scales = "free_x", space = "free_x")

Created on 2020-09-12 by the reprex package (v0.3.0)
This StackOverflow thread helped me with this answer.