The game data has a full set of sounds for indoor footsteps, they are partially done in configuration, but at end the sounds of outdoor footsteps will be used
A little configuration work needs to be done:

1. create new Sound Shader classes
2. create new Sound Sets samples for indoors wood creak
3. change existing Sound Set classes with new created Sound Shader values
4. change in existing Sound Set classes shaders for boots with values from outdoors footsteps_boots_ to indoor variants: footsteps_boots_int_

This work should be done for all 8 game-used types of indoor surfaces, these sounds are located in the folders:

• a3\sounds_f\characters\footsteps\
• int_carpet_exp
• int_concrete
• int_lino_exp
• int_mat_exp
• int_metalplate
• int_pavement
• int_softwood
• int_solidwood_exp

Example

of completed work see:
CfgSoundSets
CfgSoundShaders
and as mod variant:

https://youtu.be/Ma7SnmBd66E