Google is rolling out Memory Saver mode over the next several weeks, but not everyone will see it yet. Fortunately, if the new Settings -> Performance menu is not visible for you, you can activate it manually by using the experimental features in Chrome Flags.
Before you proceed, be sure to bookmark any important tabs and save anything important that you're working on in Chrome, then update the browser to the latest version available (109.0.5414.119 as of writing).
• Launch Chrome and paste the following into the address bar: chrome://flags/#high-efficiency-mode-available
• Next to "Enable the high efficiency mode feature in the settings", change the Default setting to Enabled, then restart Chrome
• Now paste the following into the address bar: chrome://settings/performance
• In the new "Performance" menu, toggle the switch next to Memory Saver to enable it
• Restart Chrome for the changes to take effect
Apart from Memory Saver, Google is also rolling out an Energy Saver mode that makes Chrome automatically limit battery draining tasks when the battery hits 20 percent. It does this by reducing its image capture rate and other background tasks, so you may notice changes in gaming and video performance.
The mode can be toggled on or off in the same "Performance" page in Settings. If you don't see it (this setting is only visible on portable computers) and don't want to wait for it to roll out to you, simply follow the same steps as above, but replace the address with chrome://flags/#battery-saver-mode-available and select Enabled next to "Enable the battery saver mode feature in the settings", then restart the browser.