> All licenses are perpetual (non-expiring) for the current major version, and include free minor updates.

Major version are: LINQPad 2, 4, 5, 7 and 8. The official page seems to disagree. There is nothing about LTS.

Sure, I can skip 7 and wait for 8, but that kind of defeats the purpose.

That's correct - we aim to ship a new major version every ~2 years, which for now aligns with every LTS. So LINQPad 8 will support .NET 9 (in fact, it already works with the .NET 9 previews.)