There are several options, each with their own pros and cons.
Qt [1]
The main codebase is C++, but bindings are available for Python and several other languages. I have developed and shipped multiple cross-platorm applications using Qt, using both C++ and Python. Documentation and source code examples are readily available.
JUCE [2]
Another C++ framework, with Python bindings. The focus is on music and audio apps, but a cross-platform GUI framework is also part of the library.
Blazor Desktop [3]
I have developed C# web applications using Blazor and WASM and moved them to the desktop easily. Using C# and the Dotnet ecosystem is really interesing and worth looking at.
Flutter for Desktop [4]
Still in beta, but has the support of Google, for better or worse.
JavaFX [5]
A Java cross-platform still under active development. I think it is pretty nice if you like Java.
Red [6]
Let's add an outsider just to keep things interesting!
This github site seems somewhat current about other Electron alternatives as well. [7]
Good luck! You will find there are lots of alternatives out there.
I am really looking forward to the day that I can build cross-platform GUI apps in Red. Based on Rebol, it is a beautiful yet powerful language. They are always looking for more contributors, if anyone is interested.
Edit to add: You can build cross-platform GUI apps in Red now but, while they're very close to the finish line, and making progress every day, there are still a few missing pieces yet to complete on the 1.0 roadmap.
Is there a good grid control (ie a data grid) for Blazor? A colleague reviewed the offering from Infragistics and it wasn't anywhere near their WPF data grid control.
There are grid controls from the usual commercial vendors like Radzen and Telerik. I used them briefly during a free trial. It has a funny name, but MudBlazor [1] has been the MIT licensed library I have been using lately. I have been using their Table control, which may be what you are looking for in a data grid. [2] Check it out and see.
If you have access to Python 3.5 or 3.6, you can use my open source library https://build-system.fman.io to create a Python / Qt app with an installer for all the OSs in minutes. Python 3.7-3.9 is also supported, but only available commercially.
Qt [1]
The main codebase is C++, but bindings are available for Python and several other languages. I have developed and shipped multiple cross-platorm applications using Qt, using both C++ and Python. Documentation and source code examples are readily available.
JUCE [2]
Another C++ framework, with Python bindings. The focus is on music and audio apps, but a cross-platform GUI framework is also part of the library.
Blazor Desktop [3]
I have developed C# web applications using Blazor and WASM and moved them to the desktop easily. Using C# and the Dotnet ecosystem is really interesing and worth looking at.
Flutter for Desktop [4]
Still in beta, but has the support of Google, for better or worse.
JavaFX [5]
A Java cross-platform still under active development. I think it is pretty nice if you like Java.
Red [6]
Let's add an outsider just to keep things interesting!
This github site seems somewhat current about other Electron alternatives as well. [7]
Good luck! You will find there are lots of alternatives out there.
[1] https://www.qt.io/
[2] https://juce.com/
[3] https://visualstudiomagazine.com/articles/2021/02 /17/net-6-preview-1.aspx
[4] https://flutter.dev/desktop
[5] https://openjfx.io/
[6] https://www.red-lang.org/p/about.html
[7] https://github.com/sudhakar3697/electron-alternatives