The following comment gave the correct, albeit tedious answer:
You will want to disable the extensions one by one until it drops to find out what extension is the cause here. For example, it could be that one extension was updated and now contains a crypto miner. – LPChip12 hours
This other comment gives a solution to make it less tedious to check:
Since you have a lot of extensions, you may want to not do them 1 by 1, but instead do a binary search, where you would turn off half. If the problem happens again, shut off half of what is left. If it's not, try the other half instead. Repeat until you're down to a manageable number of extensions. Also, as a sanity check, you may want to create a new profile, with no extensions, and have CHrome create an icon for it on your Desktop. Close Chrome, and open just that profile, and make sure the problem recurs. That way it's clear it's an extension causing the problem. – trlkly 11 hours ago
In my case, the CPU usage came from the Google Chrome extension https://www.grammarly.com/:
Note that to find which Google Chrome extension causing the issue, one has to restart Google Chrome after disabling the extension (because disabling the extension without restarting Google Chrome doesn't guarantee that the CPU usage will decrease: in my case it didn't, and I had to restart Google Chrome for CPU usage to decrease).