Whether you like it or not, please make use of the Menu > Help & feedback > Send feedback option in Chrome to let the devs know what you think about the bottom navigation bar. I personally love it as it puts things within easier reach of my thumb, but I know a lot of people don't particularly care for it. The Chrome team can use your feedback to help influence changes like this in the future.

For now, you may be able to control this behavior by modifying flags, but this isn't without some risk. Flags are meant to be used by developers and not us commoners; they're experimental in nature and may break or disappear without warning. They can be fun to play with and get a feel for what may be to come, but they shouldn't be relied upon as a permanent solution.

That said....

Spoiler: HERE BE DRAGONS

1. Open Chrome and enter chrome://flags#enable-chrome-duet in the address bar.
2. Change the dropdown to enable/disable the feature, or select Default to let Chrome choose on its own.
3. You'll be prompted to relaunch Chrome; do so.
4. For this one you'll actually need to exit Chrome again by swiping it out of the Recents list, and then manually launch it once more.
5. ???
6. Profit

Again, keep in mind that flags are experimental and temporary. It looks like this particular flag is currently set to be removed with Chrome v79 which will be released in December. Once a flag is removed you'll be at the mercy of Chrome once again with no way to override the behavior. So, again, SEND FEEDBACK if you're not wild about the change!