It is a bit weird that only in the first example format string is rendered in bold. As if all others are not recognized by the renderer as a valid format.

It is a bit weird that only in the first example format string is rendered in bold.

Looks as a sphinx bug.@picnixz ?

This one shouldn't be backported as 3.13 and below do not have grouping for fractional part.

Looks as a sphinx bug

That would be a Pygment issue in this case. Sphinx delegates highlighting to pygments.

Ah, indeed. Thanks.

The problem might be reported, seepygments/pygments#1340. Though, maybe it's a slightly different one.@Prometheus3375 would you like to investigate it and report to upstream?

Looks to me as the same. I will provide an additional context in that issue.

It might be different just because'_' separators were introduced in formatting mini-language later. Just a guess.

They were introduced quite a while ago, in 3.6. Nethertheless, it is not the only place where highlighting does not occur. The same happens in a couple examples below like date format and nested formatting.