Now it is clearer to me what the mainline tool does, thank you very much!
So today you could only install the Tuxinvader kernel 6.12 (when you want a later one than 6.8), the Liquorix kernel 6.16 or via the mainline tool all mainline kernels that are listed in
On this site the latest kernel is 6.17rc.
But NickS posted that he could choose 6.18 in mainline tool. So does the mainline installer offer more kernels? Where do they come from? Does the tool use also another source?