How to Expand default Layered Navigation Category Filters in Magento 2

app\design\frontend\Themes\Yourtheme\Magento_LayeredNavigation\templates\layer\view.phtml
Now, Search for the below code, you will find that code around line no-32.


<?php foreach ($block->getFilters() as $filter): ?>
                <?php if ($filter->getItemsCount()): ?>
                    <?php if (!$wrapOptions): ?>
                        <strong role="heading" aria-level="2" class="block-subtitle filter-subtitle"><?= / @escapeNotVerified / __('Shopping Options') ?></strong>
                        <div class="filter-options" id="narrow-by-list" data-role="content" data-mage-init='{"accordion":{"openedState": "active", "collapsible": true, "active": false, "multipleCollapsible": false}}'>
                    <?php  $wrapOptions = true; endif; ?>
                    <div data-role="collapsible" class="filter-options-item">
                        <div data-role="title" class="filter-options-title"><?= / @escapeNotVerified / __($filter->getName()) ?></div>
                        <div data-role="content" class="filter-options-content"><?= / @escapeNotVerified / $block->getChildBlock('renderer')->render($filter) ?></div>
                    </div>
                <?php endif; ?>
            <?php endforeach; ?>


 And replace that piece code with below-given code.

 <?php foreach ($block->getFilters() as $filter): ?>
<?php if ($filter->getItemsCount()): ?>
    <?php if (!$wrapOptions): ?>
        <?php $collapsibleRange = implode(' ', range(0, $filter->getItemsCount())); ?>
        <strong role="heading" aria-level="2" class="block-subtitle filter-subtitle"><?php /* @escapeNotVerified */ echo __('Shopping Options') ?></strong>
        <div class="filter-options" id="narrow-by-list" data-role="content" data-mage-init='{"accordion":{"openedState": "active", "collapsible": true, "active": "<?php echo $collapsibleRange ?>", "multipleCollapsible": true}}'>
    <?php  $wrapOptions = true; endif; ?>
    <div data-role="collapsible" class="filter-options-item">
    <div data-role="title" class="filter-options-title"><?php /* @escapeNotVerified */ echo __($filter->getName()) ?></div>
    <div data-role="content" class="filter-options-content"><?php /* @escapeNotVerified */ echo $block->getChildBlock('renderer')->render($filter); ?></div>
</div>
<?php endif; ?>