There could be a few different things that could be causing this issue. It could be an issue with your connection, or it could be an issue on the side of the person who shared the screen.
We don't have any control over these first two possibilities, but we can suggest turning off your VPN and getting closer to your router or using an Ethernet cable to see if that helps. The third possibility is that you may need to adjust the Hardware Acceleration option in your browser. Here is a guide on how to do that.

ハードウェアアクセラレーションのオン／オフの切り替え方法

Fire up Chrome, click the menu icon, and then click on “Settings.” Alternatively, you can type chrome://settings/ into the Omnibox to go directly there.

設定」タブで、下にスクロールして、"詳細設定 "をクリックします。

Scroll down to the System section and find the “Use hardware acceleration when available” setting. Toggle the switch and then click “Relaunch” to apply the changes.

Warning: Make sure you save anything you’re working on. Chrome reopens the tabs that were opened before the relaunch but doesn’t save any of the data contained in them.

If you prefer to wait to restart Chrome and finish up any work you have in progress, you can simply close the tab that you're using to make the changes to the Hardware Acceleration setting. Chrome will apply the changes the next time you close and reopen the browser. Just keep in mind that you'll need to close and reopen Chrome for the changes to take effect, so be sure to save any work you have open before closing the browser.