If you need something NOW, then I suppose Threads isn't your solution. You could try requesting the Expand/Collapse feature at ubbDev.com, but even that could take some time.

Maybe something like this would suit your needs.

GangsterBB.NET (Ver. 7.6.1.1)
PHP Version 8.1.34 / MySQL 5.7.23-23 / Apache 2.4.67
2007 Content Rulez Contest - Hon Mention
UBB.classic 6.7.2 - RIP