What's out there that creates timelines/gantt charts without dates?

I'm frequently creating timelines to help illustrate how i'll complete work when bidding for jobs as a freelancer, and i've taken to doing them in a spreadsheet. This is because i'm finding that all the apps I can find that can make a timeline (Notion, Clickup, etc) need the timeline to be attached to dates. However, I need to make timelines for projects with no start date (as they're speculative - not necessarily even going to happen), and I can't find anything that does that.

Looking for ease of use and simplicity above all else, especially as i'm not likely to actually use the project management tool on the project - I just need it to be able to easily create the timeline).