Hallo Denis,
On joomshaper forum we cannot support templates there are not from our Download center directly, even if they use our Helix plugin ("engine"). All templates bought somewhere else - support is from their seller/developer. It's one of main rules of Our Support Policy. This same works in Cars world. You buy a car from dealer, and he owns you support, not engine factory. If it's no longer there, well... you have to improvise or hire a good mechanic.
Let say that we talk about raw Helix Ultimate template (package) then: Template and Helix plugin should have that same version, for example, 2.0.14+ (or 2.0.15 by tomorrow).
And, Helix Ultimate 1.9 is not supported anymore, and may not work in J4.
Helix Ultimate 2.0.x uses Bootstrap 5.x, not old BT 3.x - it can affect the appearance of certain elements.
Besides Bootstrap 3.x - have major security issue(s) in javascript file, that's why is not recommended anymore. Especially now when RU hackers are only waiting for oportunites.