its probably an issue with your permalinks
go to settings → reading → permalink
now make sure this is the structure:
Screenshot 2024-02-22 at 15.19.17.png
and then click save
or its an issue with your website url
maybe you moved your website to a new server but the old website url is still in your database? i think its probably not this issue, but you can replace all occurences of your old url with the new url by using the plugin "better search and replace"