I know the .NET story much better than Java. .NET Framework support is tied to the OS support for one thing, so as long as Windows is supported, so is the corollary.NET version.
One of the values of .NET Core is that it doesn't need to be installed at all in the OS.
We are migrating away from. NET as a SaaS company. Our Monolith is in Framework and being deconstructed into .NET (current) services. It's a journey, hoping to be done in 2 years. We did successfully migrate the frontend from webforms to React, page by page. I'm sure there are other teams as well. I just interviewed a lead that was on a team doing the same thing on a Java 8 platform with a monolith.
Having just done that on a massive monolith (10y+ codebase continuously developed) I would recommend biting the bullet and doing upgrading all of your projects at once to either .NET Standard or .NET 9 where applicable. Pause development of new features or just do minimal changes on the main branch. We had a ton of footguns (EF6 -> EF Core, WPF, WCF, file serialization, multiple web services) and we were able to complete the migration in 6 months.
> so as long as Windows is supported, so is the corollary.NET version.
With Windows 11, Microsoft stepped away from their normal long-term support lifecycle. Now, you get two years or so of guaranteed support per Windows 11 release, instead of the 5+5 years even Windows 10 received.
Unless you're targeting Windows server or LTSC, depending on the Windows library may not be such a great long-term solution anymore.
The OS support isn't quite as ironclad as that. Windows Server 2019 was the last version where .NET Framework 3.5 will be supported for the lifetime of the OS; while later versions still include 3.5 as an optional feature, it's only going to be supported until January 2029 (when 2019 goes out of support), even if the OS is still in support.
We know .NET Framework 4.x will still have to be supported through October 2034 to meet similar support obligations for Windows Server 2025; but Microsoft could easily let that be the end date for 4.x if they wanted, even if Windows as a whole is still supported.
One of the values of .NET Core is that it doesn't need to be installed at all in the OS.
We are migrating away from. NET as a SaaS company. Our Monolith is in Framework and being deconstructed into .NET (current) services. It's a journey, hoping to be done in 2 years. We did successfully migrate the frontend from webforms to React, page by page. I'm sure there are other teams as well. I just interviewed a lead that was on a team doing the same thing on a Java 8 platform with a monolith.