There are a few things to know. WordPress 5.5 has new power in 3 major areas. For the official statement please read here.
Speed means that WordPress uses lazy load images unasked. Sure, this speeds up the loading time of your site. But what happens if you running an onepager?
It can be that when you using the Scroll from external URL you are not guided to the right place of your onepage site anymore because the image loads (and calculates the height of it) while scrolling. I use a plugin called jch-optimize for page speed. In this plugin i always switch the lazy load off and use optimized (what you always should do) images with Photoshop and tinypng.com instead.
Paste following code snippet to your functions.php to disable lazy load.
A sitemap XML is now included in WordPress by default. This is an amazing feature, because you can add this sitemap now directly to Google Search Console without any plugin. It will help search engines to discover your site for important content.
Auto updates for plugins and themes
Ouch! This is the opposite of security and it‘s my nightmare to lose control of my site. It means that all plugins and themes update by itself. As WordPress says: Running on the latest code.
The latest code differs from always the best code. I had plugins they remove important functions in updates and i had one (a popular one) that removes all post and custom post types in a category list in an update.
For me, doing automated updates without control is an absolutely no go. I always do a backup before updating and test it. If the backup works, then I update everything safely. If it works not, then I have another problem. This prevents me from phone calls from clients at sunday night 3 am.
The good thing is that the update settings are disabled by default. You must enable the auto update for each plugin by yourself in the plugin list.
Update themes and plugins by .zip
This is an amazing feature. bootScore and all plugins here doesn‘t have a live server. Updates so far means that you have to replace the content of the theme or plugin by yourself via ftp. Now you can upload the .zip directly in the uploader. But remember as described above: The latest code is not always the best.