There is only the observable Universe.

The Universe is closed, positively curved and asymptotically flat.

The Universe is expanding at exactly the speed of light.

This explains cosmic isotropic as 'c' has always been the same.

Derivation of the Hubble-Slipher Constant H0 given a speed-of-light expansion rate.
Kilometers in a megaparsec: 3.08567758 × 1019
One year = 31,556,926 seconds
Universe at age UAge is t = 13.8 billion years. Assumed.
Universe UAge is t = 31,556,926 × 13.8 × 109 = 4.354855788 × 1017 seconds
Diameter ct = 299792.458 km/sec × 4.3548557 × 1017 sec = 1.3055 × 1023 km
Diameter is ct = 1.305553 × 1023 / 3.08567758 × 1019 mega parsecs
Universe Diameter is ct = 4231.009 mega parsecs
Hubble-Slipher Constant is H = c per UD = speed of light per Universe Diameter
H0 = 299792.458 km/sec per 4231.009 mega parsec

H0 = 70.856 km/s per Mega Parsec