The burner domain is great for random website signups. Anything serious is done via Gmail (with two factor), but for the burner domain I use a unique address for every site that needs a sign-up (so if whatever.com needs a sign up then I use whatever@burner, other.org becomes other@burner etc etc - all addresses are directed to one inbox via a catchall) but typically the same password.
So I remember one password instead of one email address, and the address I can work out from the domain. Not exactly secure, but at least slightly resistant to leaked email lists if a site gets hacked (since every site has a unique address and common password, rather than common address and password). I am working on the assumption that people are just automatically trying leaked user-passwd pairs and won't "crack" my system... but if they do no harm done since anything important is on Gmail (I generally trust Google to not get hacked, for better or worse) and I can start again with another burner domain. For important passwords I of course use decent passwords and a password manager, but life is too short for that with websites you might only use once or twice a year and you don't really care about.
I use Zoho for the burner domain. Cheap and reliable. I tried fastmail, proton mail, and tutonova but I preferred zoho's web interface, app, and price (for the features I needed)