As was mentioned, your "big variable names" cannot be referenced ad-hoc in a formula. While I don't know if this is right (pic of data does not include enough context), I suspect all you need to do is enclose all space-including variables in backticks, as in
model1 <- lm(all_high_stat_entre ~ `Uncertainty Avoidance Societal Practices`,
             data=merged_data)
Demonstration:
mt <- mtcars
names(mt)[2] <- "c yl"
head(mt, 3)
#      mpg  c yl  disp    hp  drat    wt  qsec    vs    am  gear  carb
#    <num> <num> <num> <num> <num> <num> <num> <num> <num> <num> <num>
# 1:  21.0     6   160   110  3.90 2.620 16.46     0     1     4     4
# 2:  21.0     6   160   110  3.90 2.875 17.02     0     1     4     4
# 3:  22.8     4   108    93  3.85 2.320 18.61     1     1     4     1
lm(mpg ~ c yl + disp, data = mtcars)
# Error: unexpected symbol in "lm(mpg ~ c yl"
# x
lm(mpg ~ `c yl` + disp, data = mt)
# Call:
# lm(formula = mpg ~ `c yl` + disp, data = mt)
# Coefficients:
# (Intercept)       `c yl`         disp  
#    34.66099     -1.58728     -0.02058  
Why?
Think of this from a language-parsing viewpoint: "tokens" that are literal numbers, variables, or functions must be delimited by something. In most cases, this needs to be an infix operator, a paren, or a comma.
Examples:
- c(1 2)does not work since we want- 1and- 2to be distinct, so we use a comma.
 
- mean 2should be- mean(2), where the paren separates them. We can optionally include spaces here,- mean (2)and- mean( 2)work just fine, so the spaces here are ignored.
 
- if we have two variables - xand- y, then we can do- x + yor- x+y, where the infix- +clearly/obviously separates them.
 
In general, though, not many things (any?) in R are solely space-separated. 1 2, var1 var2, and similar are parsing errors. If we have a variable that has a space (or is otherwise not compliant with https://cran.r-project.org/doc/FAQ/R-FAQ.html#What-are-valid-names_003f), then we must inform R how to include the spaces, and that is typically done with backticks.
`a b` <- 1
a b
# Error: unexpected symbol in "a b"
# x
`a b`
# [1] 1
In some places, we can use quotes, but backticks also work.
zz <- setNames(list(11, 12), c("a b", "c d"))
zz$`a b`
# [1] 11
zz$"c d"
# [1] 12
zz[["c d"]]
# [1] 12
zz[[`c d`]]
# Error: object 'c d' not found
Noting that backticks are not always appropriate: in some locations, they push R to look for an object with that name. Had we done zz[[`a b`]] here, it would not have erred, but that's because in the previous code block I created a variable named `a b`, and that's what it would have found, then resolving it into zz[[1]] (and therefore 11).
Getting back to your case, your variable names have spaces in them. With many base R (and some packages) data-reading functions, they tend to have check.names= or a similarly-purposes argument that will convert a name of a b into a.b, but readxl::read_excel does not do that, so it allows the spaces. While I'm of mixed-opinion on which is the perfect option, I think having spaces enclosed in variable names is a risk for new users. I do like that read_excel returns a tibble, and the presentation of tibbles tends to include (for visual reference if nothing else) backticks around not-legal names. For instance,
readxl::read_excel("Book2.xlsx")
# # A tibble: 1 x 3
#   `a b` `c d`    ef
#   <dbl> <dbl> <dbl>
# 1    11    22    33
which is a clear visual cue that the first two variable names need backtick enclosures.