您可以使用将中断设置为1：12的scale_x_continuous

library(ggplot2)
library(ggthemes)
library(scales)

ggplot(rawdata4.1, aes( x= Monat, y = Ankünfte, fill = Jahreszahl)) +
  facet_wrap(~ Herkunft, scale = "fixed") +
  geom_col(position = "stack", colour = "black", lwd = 0.9, linetype = 1) +
  scale_y_continuous(labels = label_number(suffix = " Mio", scale = 1e-6),
                     name = NULL) +
  scale_x_continuous(NULL, breaks = 1:12) +
  scale_fill_economist() +
  ggtitle("Monatliche Ankünfte vor und nach Corona") +
  theme_pander() +
  theme(axis.title.y = element_text(vjust = +1.75), 
        legend.position = "right")

以可复制格式从问题中转录的数据

rawdata4.1 <- data.frame(Jahreszahl = factor(rep(c(2019, 2020), each = 24)),
                 Monat = rep(rep(1:12, each = 2), 2),
                 Herkunft = rep(c("Schweiz", "Alle Länder"), 24),
                 Ankünfte = c(647315, 1226739, 698093, 1332892, 774956, 1526592, 
                              623656, 1384180, 697684, 1624902, 858811, 2006805, 
                              987515, 2284423, 1011069, 2270490, 926890, 
                              1958831,  78940, 1612160, 589729, 1154630, 678702,
                              1381913, 707576, 1339067, 742885, 1356936, 296702, 
                              498459, 43310, 53920, 289738, 318331, 606987, 
                              725924, 1229947, 1574105, 1106300, 1545573, 
                              1021787, 1304570, 811214, 957811, 353547, 424907, 
                              484612, 603825))

问题是您使用了scale_x_binned。删除它并将Monat列转换为factor应该可以解决您的问题。
使用一些虚假的示例数据，让我们首先重现您的问题：

set.seed(123)

rawdata4.1 <- data.frame(
  Jahreszahl = rep(2019:2020, each = 24), 
  Monat = rep(1:12, each = 2),
  Herkunft = c("Schweiz", "Alle Länder"), 
  Ankünfte = runif(48, 10000, 999999)
)
rawdata4.1$Jahreszahl <- factor(rawdata4.1$Jahreszahl)

library(ggplot2)
library(ggthemes)

ggplot(rawdata4.1, aes(x = Monat, y= Ankünfte, fill= Jahreszahl)) +
  facet_wrap(~ Herkunft, scale = "fixed") +
  geom_bar(position = "stack",
           colour = "black",
           lwd = 0.9,
           linetype = 1,
           stat = "identity",) +
  scale_y_continuous(name= NULL, labels = scales::label_number(suffix = " Mio", scale = 1e-6)) +
  scale_x_binned(name = NULL) +
  ggtitle("Monatliche Ankünfte vor und nach Corona") +
  theme_pander() +
  theme(axis.title.y = element_text(vjust = +1.75), legend.position = "right") +
  scale_fill_economist()
#> Warning: Using `size` aesthetic for lines was deprecated in ggplot2 3.4.0.
#> ℹ Please use `linewidth` instead.

现在，删除scale_x_binned并转换为factor将得到所需的结果：

ggplot(rawdata4.1, aes(x = factor(Monat), y= Ankünfte, fill= Jahreszahl)) +
  facet_wrap(~ Herkunft, scale = "fixed") +
  geom_bar(position = "stack",
           colour = "black",
           lwd = 0.9,
           linetype = 1,
           stat = "identity",) +
  scale_y_continuous(name= NULL, labels = scales::label_number(suffix = " Mio", scale = 1e-6)) +
  ggtitle("Monatliche Ankünfte vor und nach Corona") +
  theme_pander() +
  theme(axis.title.y = element_text(vjust = +1.75), legend.position = "right") +
  scale_fill_economist()

像这样？

df <- tibble(
  year = rep(2019:2020, each = 24) %>% factor, 
  month = rep(rep(1:12,each = 2), 2) %>% factor,
  group = rep(c("Schweiz", "Alle lander"), 24), 
  value = sample(10000:999999, replace = TRUE, 48)
)

df %>% 
  ggplot() + 
  aes(x = month, y = value, fill = year) + 
  geom_col(position = "dodge") + 
  facet_wrap(~ group) + 
  scale_fill_economist() + 
  theme_pander()