There is a reader mode built into Vivaldi and it works okay, but on a couple of sites it seemed to truncate the text for some some reason unbeknownst to me.
Fortunately Obsidian has a built in Web reader mode too the shortcut is shown below:
Hotkeys:
| Action | Shortcut |
|---|---|
| Open Obsidian Clipper | ⇧⌘O |
| Quick clip | ⌥⇧O |
| Toggle highlighter. | ⌥⇧H |
| Toggle reader | ⌥⇧R |
If you are on Windows change the ⌘ to Win and the ⌥ to Alt.