Can't connect to iPad 3 using wifi on any hotel networks around the world but all other wifi devices connect fine. Yes I've tried all the usual fixes, reset, network reset, forget network, renew lease etc, etc. connects to home network ok ?

Have you tried turning off Safari's autofill

Settings->Safari->Passwords & Autofill->Names & passwords.

Some users have had success by doing this and deleting all the saved passwords.

You might also want to toggle off Safari in iCloud.

when you try to connect does any error show up? Does a webpage open? If not, open Safari, then go back to settings & try to connect to the Wifi network, go back to Safari & refresh the page.

If no go, make an apointment at a Genius Bar. See if your iPad can connect to their network. If it were a true hardware issue, I don't know why it would allow you to connect at home.

Do you have Private browsing turned on? That may be why it is greyed out. Is Safari's toolbar dark? With Safari open, Tap the two squares in the top right corner and in the top right of e black screen make sure 'Private' isn't highlighted. If it is, tap it to exit private browsing. Then go back to Settings & try & see if you can now turn off passwords & autofill.

Also, if Block pop ups is enabled in Safari settings, try toggling it off while trying to login to the networks.

Do you have Restrictions enabled? Settings->General->Restrictions....make sure Safari is not selected.

If restrictions is on then toggle it off (you wil need the restrictions passcode to do this )

It sounds like something in the iOS is really corrupted. At this point I would try restoring your iPad through iTunes:

Forgot passcode for your iPhone, iPad, or iPod touch, or your device is disabled - Apple Support

Before doing that & making sure Restrictions IS indeed OFF.

Try resetting your iPad by holding down the home & sleep/wake buttons at the same time until the Apple logo appears then let go & wait until the iPad boots up.

If no change, then restoring may be the only solution. I know it's a lot of work but setting up as new may be best as something in your backup may cause the same problem.

Sorry I couldn't be of more help 😟

Note: actually toggling Safari off in the Allow section of restrictions woukd remove it's access, sorry for the confusion.