Go is upgrading all the time, in 1.19,
1. set the envs, ubuntu for example: in ~/.bashrc, append lines
export GOPATH=$HOME/go
export PATH=$GOPATH/bin:$PATH
2. in go project folder
go mod init
go get github.com/cespare/reflex
3. same in project folder
go install -v github.com/cespare/reflex@latest
in this way, reflex should be able to use globally under gopath