ios 14 Mail imap

my telecom provider (scarlet in Belgium) offers an e-mail box to its clients, that I managed mainly via the Mail app on my iPhone: incoming mails via IMAP, outgoing via POP3. But after I upgraded this weekend, it wasn't possible anymore to receive in the Mail app emails from the IMAP server of Scarlet. Apple told me they have informed in time all email providers about adjustments they should make to their IMAP servers to stay compatible with the Mail app in iOS14, and that it's not their fault that my provider hasn't applied these adjustments in time. So Apple doesn't intend to send a "patch" that makes their Mail app in iOS14 treat IMAP servers the same way as it did in iOS13. But is it really a problem on the email provider side? Doesn anyone else has this problem, with another email provider than Scarlet? If yes: have you found a solution to this problem?