[system reboots and restarts of ES not logged, done where needed]
path placeholders:
(A): /opt/retropie/config/mame
(B): ~/RetroPie/BIOS/mame
(C): ~/roms/arcade/
(D): ~/roms/mame

[fresh install means := image written via raspberry imager, config.txt/dhcpcd.conf/basic retropie setup done and lr-mame2003 removed]

Szenario 1: fresh install, installed mame & lr-mame

 1.1 core options:defaults, will use B/artwork, B/samples, etc.
 1.2 core options:read config enabled, as (1.1) + B/ini/*.ini settings (excluding paths set therin)
 1.3 core options:read config + mame ini path enabled, use A/*.ini and honour settings there (including paths settings)
 1.4 core options: just mame ini path enabled, unknown so far, no settings read from A nor B (including artwork and samples).

Szenario 2: fresh install, installed lr-mame
* path A, B (and D) not created by the install. no idea from what place lr-mame would read artwork/samples/etc.; I'll bet install script and source will provide the answer (if one is used to all the variables and apis/'languages' used), but a brief scann wasn't helpfull.

 2.1 trying to identify the paths in use by lr-mame
 2.1.1 tried ~/RetroPie/BIOS/artwork -> NoGo -> removed again
 2.1.2 run rom -> core option:write config enabled -> change slider.setting, close mame
       -> no idea what was written where
 2.1.3 as 2.1.2, but with core option: mame ini path enabled -> change slider.setting, close mame
       -> again, no idea what was written where
 2.1.4 as 2.1.3, core option: read config enabled -> change slider.setting, close and restart
       -> still, no idea what was written and slider settings on defaults after restart
 2.1.5 same procedure as 2.1.4, but with core option: mame ini path disabled
       -> same result

 2.2 install mame (upstream/standalone) and place content in D and B, add vector.ini to A.
 2.2.1 start rom (asteroid) with mame from D
       -> nothing read (ini/artwork), but after closing A/asteroid.ini is written to A
          within: C as rom path (though it was started via D) other pathes are set to system/mame/[*],
       remove asteroid.ini from A.
 2.2.2.1 start rom (same) from C with lr-mame (use of mame ini path was disabled in 2.1.5),
         ... disable core option: write config, enable core option: mame ini path, close lr-mame
         -> ini and artwork was read from B
 2.2.2.2 start same rom -> no ini/artwork used....
 2.2.3+ various tryouts with (upstream) mame to no avail.

Szenario 3a: image from Szenario 1 (!last state was 1.4!), uninstall mame
* paths/files from A, B and D remain/not deleted

 3a.1 just starting rom from C -> rom/emulator not starting/falls back to ES
      -> a NoGo, no idea from where and what I can unset use mame ini path :/
 3a.2 reinstalling (upstream) mame
      -> Sigh...

Szenario ??: