The titanium Birdy is factory equipped with a 52-36 front and Shimano 105 front and rear derailleur (rear is a RD-5800-GS, front FD-R7000, the frame has a front derailleur mount for a braze-on front derailleur).

It has the current Birdy chain tensioner around the crankset chainring.

Folding is OK whatever the chainring with, as always for BIrdy with a rear derailleur and cassette, the chain on the smallest cog.

Now, the frame geometry of the TI Birdy is different from the Birdy 3 and I do not know if it will also work with a Birdy 3 with double chainring?

About the choice of the front 52-36, with the small wheels of the Birdy, 36t front gives really short gears, I never need the 36t front + 32t rear I have. A 53-39 combination is probably better.

The original gearing of the Ti Birdy (and R20 SP 11) with only a 11-28 cassette is not a good choice (gearing too long for hills on the 28t, too short on flats with the 11t). Its probably the reason why Pacific Cycles mounted a front compact crankset and front derailleur on the Birdy Ti. The 9-32t cassette range of the R&M Birdy touring is a much better choice.