We aren’t providing any more patches for Acorn 6 (it came out in 2017), and I really, really wish Apple hadn’t broken receipt validation for older apps.
Acorn 6 isn’t 100% compatible with Tahoe, either - but if you want to give it a try I can maybe figure something out. Shoot me an email at support@flyingmeat.com referencing this post, and I can see about making a license for you for the direct version of Acorn 6.