Hi GSE,
On the left side you have SP Page Builder 3.8.x on the right side probably SP Page Builder 4.0.x interface, there are big difference between those versions.
If you want to have back-end editor keep SPPB 3.8 on your sites. SPPB 4.x have only front-end editor.
- SPPB 3.x will be supprted for next two years.
- The only safe & recommended way to downgrade SPPB from v4.0.x to 3.8.x is to use full website backup from day before you installed SPPB 4.0.x. I mean you have to recover whole website. But remember to delete (!) components/com_sppagebuilder folder before, to not keep SPPB 4 files.