They have a docker instal option. Granted it’s a bit of overkill but you can run it like desktop software.
Having Docker and other "enthusiast" methods of running software makes it less accessible. Having a web-stack as the goto method of writing software doesn't make sense if it limits the audience that would gain value from it.
I say this as someone who professionally maintains a web application that comes with a Windows installer, macOS traditional installation and a Linux RPM. All with desktop icons and it being pretty invisible to the user that it is a web application aside from the HTML-looking UI style.
The software is for personal finance, it isn't for a niche that makes the install/access method particuarly sane. If it were software for managing a cluster of X-thing or something ... maybe.
I'm curious; how do you implement this (I assume you do not use Electron)?
Wouldn't a PWA (installed PWA) make the web app integrate the way you say with desktop icons, separate window, drag & drop etc?
The binary is built for those OS and installed via installers idiomatic for those systems.
It defaults to use a local sqlite backend but could use any rdbms. Simple really.
Slapping a web server into a local desktop install and calling it good basically removes the vast majority of benefits of it being a web app.
But you can also launch it with "--serve" options to access it through a web browser and expose it on a network, with sqlite local disk database.
You can also launch with "--db=postgresql://postgres@dbhost:5432/postgres?sslmode=disable" to run it against a postgresdb.
A bit of work on the "how it runs" aspects can give great flexibility and usability for single-user cases.