Cloudflare Email Routing: How to set up `+topic` custom addresses?

I want to set up a custom address with + symbol in it, e.g. someone+sometopic@my.domain.
Firstly, I tried setting up this address directly by creating a custom email address in the dashboard but was blocked by the validation logic indicating that allowed characters in the address are 0-9 a-z _ . (as shown in the screenshot).
Then I tried to create a custom address without the topic (i.e. someone@my.domain) and expected Cloudflare Email Routing would follow the same rule for the address with the topic (i.e. someone+sometopic@my.domain), as Gmail does (https://support.google.com/a/users/answer/9282734?hl=en#email-address-variation); but testing showed someone+sometopic@my.domain just matches the catch-all rule, so no luck.
So is there a way to use custom email addresses like someone+sometopic@my.domain with Cloudflare Email Routing? Thanks in advance.
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