Access nextcloud via external ip works in windows laptop but not ubuntu linux unless i connect to a hotspot instead of local wifi

I can use my windows laptop to browse my nextcloud on local wifi via the router and also using my freedns address; and I can browse to it using the local IP address of the pi. BUT using my ubuntu linux laptop, I can’t browse to my nextcloud using the external IP or freedns address. I can SSH to the pi alright, and I can ping the freedns address which resolves to my internet IP, but the browser just says it is unable to connect (unless I use a wifi hotspot)
can anyone explain simply and tell me what to do?