I am not able to install RStoolbox packages in Ubuntu

Please do not post screenshots, it is considered a bad practice here, post the console output as formatted code instead, here is how to do it:

Now about your issue, you are showing a very different error message now

#> free() invalid pointer 
#> Aborted
#> ERROR: loading failed

it seems your system has fallen into a bad state I would try restarting the whole thing (Just closing the console doesn't restart WSL2) and trying to install rgdal again.

For Ubuntu 20 the RSPM repository has a different link, you can try with this

install.packages("rgdal", repos=c('https://packagemanager.rstudio.com/all/__linux__/focal/latest', 'https://cran.rstudio.com/'))