I came here looking for solutions to that problem. The only sleeve that works properly for me is the Turbos. Even the one that came with the Keon rubs for me. I found this elsewhere and am going to try it out later. Hopefully it helps
https://www.reddit.com/r/Kiiroo/comments/mni21u/using_fleshlight_sleeve_in_keon_may_not_be_worth/
This might be a solution too, but I don’t have access to a 3D printer
https://www.thingiverse.com/thing:4899504
If you have an extra Keon case (I don’t) possibly cut it so it can snap on over the part that bulges outward