fixed back round image on mobile version

background-attachment: fixed is not supported by most of the mobile devices.
So Enfold turns that to background-attachment to : scroll – and a parallax container is generated.

A position fixed is supported by mobile devices – the trick is to tranform that.

Important: so set the background-attachment on that color-section to scroll please!
give a custom class to that color-section : bg-fixed and put this to your quick css:

.avia-section.bg-fixed {
  -webkit-clip-path: inset(0 0 0 0);
  clip-path: inset(0 0 0 0);
  background-size: 0 !important;
  overflow: hidden;
  position: relative !important;
}

.avia-section.bg-fixed:before {
  background-image: inherit !important;
  background-repeat: inherit !important;
  background-size: cover;
  background-position: inherit;
  content: "";
  position: fixed !important;
  width: 100%;
  height: 100%;
  top: 0;
  left: 0;
  z-index: -1 !important;
  will-change: transform;
  pointer-events: none;
}

see f.e: https://webers-testseite.de/goodwave2/
PS: kanst du mal auf deiner Seite : was_mich_2_jahre_haarefaerbens_gelehrt_haben schauen, die Bilder sind eingeladen über:
i0.wp.com – war das deine Dev Seite, die du migriert hast? Jetzt hast du eine Rückbezüge auf diese Seite, das ist mixed Content bewertet – ausserdem ist die http – weshalb die Seite dann auch als nicht sicher eingestuft wird.

where can i see that page where you have changed it?
i do know your domain from former topics so if you like to say only the page i will find it.

Here it works :
/biologique-recherche-und-warum-es-suchtig-macht
/was-mich-das-zusammenziehen-gelehrt-hat/

i will now test it on real devices – but on all my browsers in mobile simulation it works.

next – strange behavior: if i use the minimum-height option with 75% from enfold ( removed the custom-class : fullheight with its vh setting in quick css ) – it works too !
i only can reproduce the effect ( from your film on top ) that the last “fixed” pseudo-container is seen and background-colors of other containers – are gone when using that 100% setting.

PS: even a minimum custom-height of 99% will do the job – without css height – only with bg-fixed substitution. ??? – why not the 100%

yes

Or just set this in addition to the bg-fixed rules:

.avia-section.bg-fixed.av-minimum-height-100:not(.av-slideshow-section) .container {
       height: 100vh !important
}

so – you can use all the other minimum-height options on enfold – and if you use the 100% value the rule above does force the other setting.

on that page: /sonnenschutz_und_was_ihr_dazu_wissen_muesst you got fixed setting – not scroll on attachment. !!!

Important: so set the background-attachment on that color-section to scroll please!

the same on /was-mich-das-zusammenziehen-gelehrt-hat with #av_section_3

on /warum-weiss-die-ultimative-farbe-ist and
/sind-gesichtssprays-wirklich-hilfreich/ i do not see your error.
What kind of iphone is it – is it realy older than the one i tested this for you: iphone 6s with iOs 15.5 ;)