Joy
(@joyously)
The typical problem for this is a plugin or a widget in the sidebar, that lists posts but doesn’t reset the query for the pagination to work correctly. But I don’t see anything but core widgets in your sidebar.
It looks like your theme has some issues, though. Is it outputting the SVGs or is that a plugin? There are numerous </noscript> tags that are extra. (It looks like it is output twice every time it is output.)
There is also a </use> when that is a self-closing tag.
There is also a link nested within a link, but that is invalid HTML.
You can run your page through a validator, to help you find the various problems.
Also, the sidebar is at the bottom with a window of 1240px width. That’s wider than a lot of laptops.
To be honest, I have no idea about much of this stuff. I inherited the website from the previous marketing agency we had been using. I’m not sure what they did upon setup and I’m hesitant to change anything lest I break it, which is why I’ve come here to ask rather than start tweaking things.
I’ve give the validator a try and see why types of fixes it recommends.
Otherwise, I’ve not got the foggiest idea of even how to go about checking the things you pointed out, but I’ll google it and see what comes up.
Joy
(@joyously)
For fixing the theme, you could try going into the Customizer and previewing your site with other themes. It should be simple to switch to a better one.
If the SVG stuff is in a plugin, however, then you need to ask at the plugin’s support forum.
You can try the Health Check plugin in Troubleshoot mode, which allows you to disable plugins for your user only without affecting site visitors, so you can determine if the paging problem is a plugin or theme.