I posted this over on dlsc-software-consulting-gmbh/jfxcentral2#692 which is homepage for JavaFX development. It uses JPro to present the content to the browser.
I also noticed the main homepage of JPro itself (https://www.jpro.one) also doesn't open links on the page by clicking on them. I need to right-click and select open in new tab from the context menu. Otherwise, no link processing seems to be working.
Everything works ok in Firefox, so it's something in Safari 26.x that doesn't seem to be handled.
I've turned off all popup/ad blockers and make sure that links open in new tabs, etc.. just as I did before the upgrade to MacOS 26.