We have multiple Kentico Xperience 13 sites running on .NET 6 without any issues.
Yes, minimal APIs/startup is not supported with Kentico Xperience 13 (I'm the one who identified those limitations to the support team when upgrading a site), but everything else in ASP.NET Core 6.0 works fine.
.NET 6 brings performance improvements, C# language enhancements, and a faster development workflow with .NET hot reload.
You are correct in understanding that it's better to be on an LTS version of .NET than a non-LTS if the non-LTS version is nearing end-of-support. But besides that, the .NET community is already getting used to yearly upgrades so if you want to stay inline with what's supported by the community I'd recommend upgrading your .NET version within 6 months of each new release. This is the modern .NET way.