I mean the bme68x.c file you used.
You could download BSEC 2.x Software from https://www.bosch-sensortec.com/software-tools/software/bme688-software/ and test "BSEC_22.214.171.124_Generic_Release_04302021\examples\bsec2\examples\basic_config_state".
If you also have same temperature difference, then we will check it.
We do have some temp offset due to self heating.
Technically, you should put offset value using BSEC_INPUT_HEATSOURCE, but some version you should put it manually after you get some temp data.
We already recognized the issue and will release fixed version later.
Thank for your reply.
I'm using "...\Bosch-BSEC2-Library-master\examples\generic_examples\basic_config_state\basic_config_state.ino for my test.
I'll try your recommended file soon.