Clustered column chart for single cell data
You can make use of table() and prop.table() to calculate the number and proportions of your cell types with respect to tissue of origin.

prop.table() requires a table as input so you can start with something like prop.table(table(object@meta.data$cell_type, object@meta.data$tissue). This will create an objet of class table.

Next step is to create a data frame with as.data.frame(your_table_object) and then to convert it to "long format", for example with tidyr::pivot_longer(). You can feed these data in long format to ggplot().