Thank you for the suggestion. I didn’t know about Logitech Options until you mentioned it, and it’s not installed on my machine. After reading about it, it does seem like it interferes with application controls. This failure to go back or forward is a new phenomenon dating back some several days. I don’t know exactly when it began since I probably dismissed it earlier as a fluke. But now it’s obvious that it’s only the Brave browser that has this problem.
I must add that the problem has stopped. This morning I discovered other faults and realized that maybe the problem was that I had not restarted Brave in several days. I closed all my Brave windows and restarted the program and everything works as intended. I will remember this the next time something odd happens. Thank you for your time spent thinking about this matter.