Apple had released iOS 13.4.5 Developer Beta 2 on April 15th, alongside the press release of the iPhone SE (2nd Generation) and the announcement of the availability of the Magic Keyboard for the iPad Pro. Apple has also released the Public Beta version for this version (iOS 13.4.5 Public Beta 1). Apple did not release the Public Beta version with iOS 13.4.5 Developer Beta 1 released to developers on the 31st of March 2020.
Apple had already released iOS 13.4.5 Developer Beta 2 / Public Beta 1 for the iPhone SE (2nd Generation) on April 15th. The build number for iOS 13.4.5 Developer Beta 2 / Public Beta 1 is 17F5044d. Once you receive your iPhone SE (2nd Generation, it will be running iOS 13.4 out of the box. You can install the Developer Beta Profile through Apple’s Developer Portal or the Public beta Profile from www.beta.apple.com.
The build number for iOS 13.4 running on this device is 17E8255 while the build number for iOS 13.4 running on other iPhones, iPads and iPod Touch is 17E255.
Apple has also released iOS 13.4.1 for the iPhone SE (2nd Generation). Read more about it here.