EU Settlement Scheme (pre-settled) application with non-EU passport & family permit

Applying to the EU Settlement Scheme (pre-settled status) with an EUSS Family Permit and non-EU passport.

Unsure about the sequence of these steps...
- submitting an application online (UKVI)
- biometric appointment (UKVCAS)
- sending the passport (some say it is necessary, others say not)
- uploading evidence (UKVI)

I only know one has to apply before the family permit expiry date (in my case 19/4/2022 !), however what does it mean "to apply" ???
- to submit an application online ?
- to have biometrics done ?
- to upload all the evidence ?

I am concerned about the upcoming bank holidays (15/4 and 18/4) and closure of UKVCAS locations.
Also still waiting for some evidence (NHS and NIN letters). Should I apply without them and perhaps send them later ?

Can anyone advise me what happens after I click "CONFIRM AND CONTINUE" (as shown on the screenshot) ?
What will be the outcome / next step ?
Why do they require a strange declaration after only an initial stage of the application (no uploads yet) ?
THANK YOU !