Think Twice Before Activating Two-Factor Authentication on Vivaldi

I have been using Vivaldi Mail since the company was founded, trusting in Jon von Tetzchner (former Opera founder, now Vivaldi Technologies), glad for a reliable alternative to Gmail. Around two years back, Vivaldi announced that their account now supported 2FA. But when I checked it out, it came with an omnious warning that you could lose access to your account permanently if any of the 2FA method failed. So I avoided it for nearly 2 years till I succumbed to the security fearmongering of using 2FA (or else!) and enabled it a few months back. Long story short, both TOPT and Recovery Codes today suddenly stopped working on my Vivaldi Account (I have no idea why - it just says "Authentication Failed!"), and I cannot access it anymore. Vivaldi support says I have now lost access to my account permanently, and they cannot do anything. So now I am in the ridiculous situation of having access to my emails through IMAP, from an email client (through which I can still send and receive mail) but can't access it through a browser and am denied total access to change any setting on it (like disabling 2FA or change my password)! My account has an alternative email, my phone number and I think even security questions (all of which Vivaldi insists on) and can be used to verify I am who I say I am, but apparently they still cannot do anything to grant me back access to an account I've used for maybe 10+ years now. I am at a loss on how to deal with such convoluted, broken, online security measures ...