Suite 8.0 es5 support plan

Currently using suite 8.0 version

I am contacting you because there is an es5 compatibility problem

And if compatibility is difficult, we ask if it is possible to change the product to a lower version.

Could you please, clarify what compatibility problems do you mean?
As far as I know, there are no issues with the ES5 compatibility in the dhx.Suite 8.

Perhaps my question has been misunderstood.
We need to support the IE11 environment for our current customers. However, some functions used in the suite8 version (for example, .remove(), etc.) were not recognized in IE11, and an error occurred.

ahh, I see.
Yes, dhxtmlxSuite 8 (6+ actually) does not support IE11.
In this case I can only suggest you to use the dhtmlxSuite 5.
As this build is deprecated and not supported anymore it is not available for the direct download.
You may try to contact our sales to request it: