Pennywise might be a bit more popular than Duplicate Windows. We know about 1 link to it since March 2021 and only 1 link to Duplicate Windows. We are tracking product recommendations and mentions on various public social media platforms and blogs. They can help you identify which product is more popular and what people think of it.
I haven't used this personally, but it may get you some of the way there: Duplicate Windows app. Source: about 1 year ago
Afloat - Don't know if it will work for macOS 12. If it's just for safari alone, you can try Pennywise. Source: about 2 years ago
Afloat - Create beautiful invoices in 3 clicks, without mistakes
Helium - Helium lets you accept payments by credit card for anything you want to sell online.
PiP for Mac - Always on top window preview similar to the popular windows only OnTopReplica
PiP-Tool - PiP tool is a software to use the Picture in Picture mode on Windows.
PiPer - A DIY Minecraft computer to build gadgets
Picture In Picture - Picture In Picture comes as an extension tool that enables users to watch videos in a floating window.