@plop6901 ,

Please don't use the old classic theme with wpForo 2.0. This theme will not be supported very soon and all your issues will be left without any help. All wpForo 2.0 features are only available with the new 2022 theme. There is no mean to use wpForo 2.0 with the outdated old classic theme.

Again this is the last help we provide for your issue, you can put this CSS code in wpForo > Settings > Color and Styles > Custom CSS Code textarea, delete all caches and check it:

#wpf-widget-search #wpforo-search-form .wpf-search-widget-label input[type="text"] {
  position: relative !important;
  display: block !important;
  padding: 7px 8px;
  height: 32px;
}
#wpf-widget-search #wpforo-search-form .wpf-search-widget-label svg {
  enable-background: new 0 0 16 16;
  fill: #999;
  position: absolute;
  width: 19px;
  height: 19px;
  right: 5px;
  bottom: 6px;
  cursor: pointer;
}