Hi @Attila,
While I wish we could offer more at this time, the short answer here is that tablets aren’t officially supported with ARC yet, although they’re often functional for many.
That said, I would recommend attempting to change the default browser on the iPad, in case the adblock settings are hanging authorization redirects after logging in.
You can vote on the iPad feature suggestion here: Roon ARC on Tablets (iPads and Android) [On Roadmap]