Using numbers with decimal points in if statements and operators

I'm trying to write a script that detects the Linux OS and version and through the use of conditions and operators execute different commands depending on the result. **Detect OS**

if [ -f /etc/os-release ]; then 
	. /etc/os-release 
	OS="$NAME" 
	OS_version="$VERSION_ID" 
elif [ -f /etc/debian_version ]; then 
	# Older Debian/Ubuntu/etc. 
	OS="Debian" 
	OS_version="$(cat /etc/debian_version)" 
fi

If I echo these variables they return with

$ echo $OS 
Debian GNU/Linux

$ echo $OS_version 
10

In my example below I want to match **Debian** and OS version **10**. However, the **$OS** variable contains more that just the word **Debian** so I need some kind of wildcard so I can do a partial match. The only way I've found to get this to work in through command substitution by echoing the **$OS** variable to stdout and piping it into the grep command which then does a wildcard search. This is the if statement I came up with in the end:

if [ "$(echo "$OS" | grep 'Debian*')" -a "$OS_version" -ge 10 ]; then 
	echo "OS is Debian" 
	sleep 4 
else  
	echo "OS is other" 
	sleep 4 
fi

As I will be using this script on other Unix based OSs so I would like to make this script as widely compatible as possible and stick to POSIX standards. While testing my script on Ubuntu 21.04 I discovered that Linux has trouble working out which number is greater than another when there is decimal place involved. Below I've created two shell scripts which export a two-integer number with a two-decimal place and uses an if statement to check if it's greater and/or equal to another number. **20.10.sh**

#!/bin/sh
export OS_version="20.10"

if [ "$OS_version" -ge 21.04 ]; then
    echo "Your OS is new enough"
    sleep 2
else
    echo "Your OS is too old!"
    sleep 2
fi

**20.10.sh output**

~$ ./20.10.sh 
YOUR OS VERSION IS >> 20.10 
./20.10.sh: 6: [: Illegal number: 20.10 
Your OS is too old!

**23.45.sh**

#!/bin/sh
export OS_version="23.45" 
if [ "$OS_version" -ge 21.04 ]; then 
    echo "Your OS is new enough" 
    sleep 2 
else 
    echo "Your OS is too old!" 
    sleep 2 
fi

**23.45.sh output**

~$ ./23.45.sh 
YOUR OS VERSION IS >> 23.45 
./23.45.sh: 6: [: Illegal number: 23.45 
Your OS is too old!

The **23.45.sh** script should echo "Your OS is new enough" but doesn't and displays an error of an illegal number. Is there a way to detect the size of different numbers with decimal places in?