To make checklists more readable in Obsidian after completing items, this CSS snippet removes the strikethrough. Store it in [YOUR_VAULT]/.obsidian/snippets/checkboxes.css.

/* These two affect preview mode */
.markdown-preview-view ul > li.task-list-item.is-checked {
  text-decoration:none;
  color:var(--text-normal);
}
 
.markdown-preview-view ol > li.task-list-item.is-checked {
  text-decoration:none;
  color:var(--text-normal);
}
 
/* This affects edit mode */
.markdown-source-view.mod-cm6 .HyperMD-task-line[data-task]:not([data-task=" "]) {
    text-decoration:none;
    color: var(--text-normal);
}