Watching a fixed gear rider on platform pedals is like watching an automobile race. You can't look away because you know there will be a crash any second.
Or, the rider knows he can't stop for ****, so is riding slower than a grandma.
Either way, don't do it. Use toe clips at least. Clipless if possible.
I ride my fixed on flats without retention. I have toe clips and straps on my gravel bike. I ride further and faster on my fixed and have never had an accident on it or had my feet fly off the pedals. As with all things, you can practise and do, or you can buy more stuff.