library(tidyverse)
library(mapview)
library(sf)

lat <- rep(34,20)  #sample latitude
lon <- seq(-128, -126, length = 20) #sample longitude

set.seed(1)
value <- rnorm(20, 0, 6) #20 values: some positive, some negative

#make data.frame
df <- data.frame(lat,lon, value)

#make spatial object for mapview
df <- st_as_sf(df, coords = c("lon", "lat"), crs = 4326) %>%
      mutate(value_abs = abs(value)) #value_abs intended for `cex` argument

pal <-  mapviewPalette("mapviewSpectralColors") #from mapview doc. example
m   <-  mapview(df["value"], #hover over value
         cex = "value",      #circle diameter value
         legend = TRUE,
         col.regions = pal(100), #closest I came to achieving a red-blue divergent scale
         layer.name = "value")
m