When to use Argon2i vs Argon2d vs Argon2id?
If you are unsure, then always choose Argon2id. Only choose Argon2d if you need maximum security at the expense of side-channel risk, and only choose Argon2i if side-channel attacks are the primary threat.

The number of passes just increases resistance to time-memory tradeoff attacks (TMTO). What you are probably remembering is that Argon2i is more vulnerable to TMTO attacks, and thus needs more passes to obtain the equivalent level of security. Argon2id uses the Argon2i pass to resist side-channel attacks, and the subsequent Argon2d passes to make up for TMTO resistance that the first pass lacks.

If an attacker performs a perfect side-channel attack and breaks the Argon2d portion, then they will still need to perform a very extensive TMTO attack to break the Argon2i passes. Compare this with pure Argon2d, where a successful side-channel attack completely negates its memory hardness. In other words, a side-channel attack against Argon2id reduces its security to one-pass Argon2i.

Note that some of the more severe TMTO attacks against Argon2i have actually been fixed.