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 There is no mean to use wpForo 2.0 with the outdated old classic theme.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. Please remove the CSS code provided above, it removes the search button in the search field. There is a better solution, you just need to make it smaller and show in the search filed. The button need for clicking and submitting the search phrase.

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 {
    position: relative !important;
    display: block !important;
}
#wpf-widget-search #wpforo-search-form .wpf-search-widget-label input {
  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;
}

use this css code:

#wpforo #wpforo-wrap label.wpf-search-widget-label svg {
    display:none;
}

provide forum URL.