No, dual booting won't slow down your system. Here are many more dual boot myths that you should not believe anymore.

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Dual booting allows you to have two operating systems on a single computer, and switch between them at boot time. Despite common myths, it does not slow down your system, is not limited to Windows and Linux, can be done with secure boot enabled, does not require two disks, doesn’t necessitate installing Linux after Windows, and you can revert to a single OS without formatting the entire system.

Don't Believe These Dual Boot Myths

2. Dual Boot is Only About Windows and Linux

4. You Need Two Disks to Dual Boot a System

5. You have to install Linux after Windows

6. You Cannot Go Back to Windows Without Formatting The Entire System

I’ve dual booted Windows with Linux for years. One of the biggest annoyances that I’ve encountered is bluetooth pairing. Because of the way it works, you won’t be able to pair some devices with 2 operating systems without jumping through some hoops to move the pairing keys from one system to the other.

For most people I would say using WSL is better - you have windows and linux at the same time and they can share file system resources easily. WSL 2 was a huge improvement over WSL 1, so if you’ve not tried it recently take a look again.

WSL is so good now that there is not much purpose in dual boot. Especially for developers, you can just install WSL and Write all your projects in your Linux environment without rebooting. VS code even has a WSL mode so you can run your Linux projects through WSL on your Windows machine using VS code. No more partitioning drives so that you can dual boot just to realize that you gave one machine too much or too little storage. WSL just uses your main drive dynamically.
TLDR: Use WSL instead of dual boot

The only reason I don’t dual boot anymore and instead use a vm is because I keep bricking my linux installs 😅 But everything else in the article is on the money. Never had any issues with dual booting (other than the aforementioned incompetence.)

I have been dual booting linux and windows 11 for almost 3 years now i have never encountered issues with speed or any other issues except my windows 11 OS keep writing my grub whenever it automatically updates but yeah this is very unlikely to happen for most users.