Keep in your own hard disk ?

What are you expecting, when you don't want to use a code version control system. Just store it in your own storage devices.
If what you mean is you don't want to store into a public SVC system, you can always setup your own. If you just want a repo local to your system, you don't need to push into a remote GIT, you can just keep your source code tracked locally
Once your perform a "git init", all commits to the code are already locally tracked. You can simply just tar up the whole parent directory that contains all your numerous local git repos and store it elsewhere as backup.
Code:
$ git init project1
Initialized empty Git repository in /Users/davidktw/WORK/GITDEMO/project1/.git/
$ cd project1
$ echo def > abc
$ git add .
$ git commit -a --allow-empty-message -m ''
[master (root-commit) 46ad841]
1 file changed, 1 insertion(+)
create mode 100644 abc
$ git log
commit 46ad841480cf34f5c58135df738a5bddb343466f (HEAD -> master)
Author: XXX <YYY>
Date: Wed Mar 24 16:51:59 2021 +0800
$ cd ..
$ ls
project1
$ git clone ssh://davidktw@localhost:/Users/davidktw/WORK/GITDEMO/project1 project2
Cloning into 'project2'...
Password:
remote: Enumerating objects: 3, done.
remote: Counting objects: 100% (3/3), done.
remote: Total 3 (delta 0), reused 0 (delta 0)
Receiving objects: 100% (3/3), done.
$ ls
project1 project2
$ cd project2/
$ git log
commit 46ad841480cf34f5c58135df738a5bddb343466f (HEAD -> master, origin/master, origin/HEAD)
Author: XXX <YYY>
Date: Wed Mar 24 16:51:59 2021 +0800
$ ls
abc
$ cat abc
def
Simple demonstration to you that all you need is a *nix box and you can just store your projects in it. You can easily just clone out from another simple using ssh to connect to a remote repository which is as simple as a remote *nix box. There is no extra software you need except installing the GIT.
Have fun.