I second that:

I would love to see additional options in the custom section, particularly for incorporating various breathing exercises such as square breathing/ pranayama. This would allow users to create a playlist of different breathing exercises, seamlessly combining them into one session without needing to manually start a new table each time.

Example:

5 minutes of 10s inhale / 10s exhale

Followed by 5 minutes of square breathing with a 10s-20s-20s-10s pattern

Followed by another 10 mn square breathing session with a 10s-1m15s-10s-4s pattern

Additionally, having the flexibility to include any type of exercise (O2, CO2, square breathing, etc.) in these sequences would be fantastic.

Ooh I like this idea

That would be great! I like to start with a warm up like 30sec, 1:00min, 1:30min and then do a CO2 table.