Learn English – “When it comes to doing something” Are there alternatives

If and when carries no direct formality implication as your search shows.

Note 1: Unless you associate the complexity and precision with formalism. As in if you assume that a formal audience will more likely understand (and also correctly use) the expression in all of its subtleties.

Note 2: The phrase was actually heavily criticized by Fowler (see here) and perhaps more appropriately treated in Merriam-Webster. This complexity is something that you might not want to deal with in informal text or talk.

To "catch up with" is considered--currently at least--informal but standard English. More formal English would be "let us set up an appointment". However, if this is an informal setting, meeting a friend, then "catch up with" is fine.