Permalinks have duplicate sub-directory; ok some time ago!

Hi! I’m new with WP. My Permalinks all have a duplicate sub-directory named ‘welcome’. My .htaccess file shows a base without this ‘welcome’. So something changed that caused this. How does one change ALL urls in the Permalink listing? The one plugin what ask what url to use? This is the one place that ‘welcome’ appears on my site. ‘welcome’ was removed from plugins settings but still showing in Permalinks page. What else may I do to delete ‘welcome’ from showing up in mu Permalinks page?

See the problem on my webpage https://fortranCalculus.info/textbook/welcome . This page should only have one ‘welcome’ and it does. Click on ‘About’ link under the ‘welcome to …’ header menu and this shows two ‘welcome’ in its path/url. Need Help!

ALL my permalinks show ‘welcome’ in their urls as shown here … https://fortrancalculus.info/textbook/welcome/ … this ‘/welcome’ needs to be removed, how?

Thanks, Phil