Stack Overflow used to have 'disable responsiveness' option at the bottom of the screen ... Is there a way to do that on Code Review?

No, not that I'm aware. As far as I know, that setting was a temporary solution implemented somewhere around 2018 that could be used while they were making the entire network responsive. That has been done, so the old pages are no longer maintained.

However, you can get rid of the left bar. That's the navigation bar mentioned in the settings:

As you've found yourself, there's a similar setting hiding the Hot Network Questions. But that still leaves that column in use by other components.

Most of the whitespace can be removed by zooming in, but this could depend on your browser, device or settings. For example, looking at the answer you got your picture from, this is what I can that specific part look like on my monitor:

That's on a fairly standard 16:9 monitor.

The size is starting to look silly, but it has more space actually in use than it had. Unfortunately, that's about as good as it gets.

If you want to remove more, you'll have to go the unsupported route and dig into userscripts. There are a number of userscripts available, written by community members, on Stack Apps. For example, here's a list of all questions mentioning hide. For example, this script claims to remove some links from the Community Bulletin and this script claims to remove certain sites from the Hot Network Questions. In theory it's possible to create a userscript that hides a lot more. I do not know the limitations and, again, this method is not supported. And by not supported, I mean a lot of regulars are depending on it quite a bit.

Note: there are many more ways to find userscripts to your liking. For example, Violentmonkey has a page for Stack Exchange sites and GitHub has a lot of them as well.

Stack Overflow used to have 'disable responsiveness' option at the bottom of the screen ... Is there a way to do that on Code Review?

No, not that I'm aware. As far as I know, that setting was a temporary solution implemented somewhere around 2018 that could be used while they were making the entire network responsive. That has been done, so the old pages are no longer maintained.

However, you can get rid of the left bar. That's the navigation bar mentioned in the settings:

As you've found yourself, there's a similar setting hiding the Hot Network Questions. But that still leaves that column in use by other components.

Most of the whitespace can be removed by zooming in, but this could depend on your browser, device or settings. For example, looking at the answer you got your picture from, this is what I can make that specific part look like on my monitor:

That's on a fairly standard 16:9 monitor.

The size is starting to look silly, but it has more space actually in use than it had. Unfortunately, that's about as good as it gets.

If you want to remove more, you'll have to go the unsupported route and dig into userscripts. There are a number of userscripts available, written by community members, on Stack Apps. For example, here's a list of all questions mentioning hide. For example, this script claims to remove some links from the Community Bulletin and this script claims to remove certain sites from the Hot Network Questions. In theory it's possible to create a userscript that hides a lot more. I do not know the limitations and, again, this method is not supported. And by not supported, I mean a lot of regulars are depending on it quite a bit.

Note: there are many more ways to find userscripts to your liking. For example, Violentmonkey has a page for Stack Exchange sites and GitHub has a lot of them as well.