Is Bitdefender or Proton VPN compatible with iMac/MacBook M4?

If you want to make your computer unstable, slow, appear buggy then yes please install each.

In all seriousness, Mac OS does not require or benefit in ANY way by installing any of the following types of third party apps because Mac OS does EVERYTHING these days apps purport to do. What these apps do is modify Mac OS and make it appear unstable and slow! If you search these forums you will find thousands of posts from users that have made a mess of their Macs by installing these and similar apps.

• Antivirus
• VPN
• Security
• Cleaning
• Maintenance

In short, please do not consider or install ANY of these types of third party apps!

+1 You don't need any third-party protection junk-ware with macOS.

see > macOS - Security - Apple

In addition to all of the great information already provided, you may want to read this:

Effective defenses against malware and ot… - Apple Community

Don’t.

Using a VPN to access the Internet does nothing to protect your privacy or secure your data.