To add keyword filter to Gallery Block, you can can use this plugin.
#1. First, purchase plugin and paste the link to Page Header Injection (page where you added Gallery Block)
#2. Click Get Filter Config
#3. A Popup will appear. Click COPY CODE
#4. Remove code in #1, and add code in #3.
#5. Edit Gallery Block > Click Design > Enable Show Title
#6. Result
#7. To change these titles, just hover on Image > Click Gear icon
add it here
#8. To remove title under image, add this code under #4 code
<style>
.custom-filter-item .image-slide-title {
display: none;
}
</style>