The new assembly improvement also ignores synthetic pop cap. If you want to mod it in, here is the old assembly project. Thanks due to Tetrasodium. His post on the issue: https://forums.galciv3.com/461091/page/1/
Should still work assuming they haven't removed the GrowthYor variable yet. Hopefully it stays in as an artifact just for this purpose. I personally prefer adjusting the values by dividing by 100, produces a better curve for the growth as suggested by someone that I can not recall atm, apologies.
<PlanetaryProject>
<InternalName>ProjectAssembly</InternalName>
<DisplayName>PROJECT_ASSEMBLY</DisplayName>
<ShortDescription>PROJECT_ASSEMBLY_DESCRIPTION</ShortDescription>
<Icon>GC3_Colonization_Icon.png</Icon>
<ManufacturingPerBonus>10</ManufacturingPerBonus>
<Bonus>
<EffectType>GrowthYor</EffectType>
<Target>
<TargetType>Colony</TargetType>
</Target>
<BonusType>Flat</BonusType>
<Value>0.2</Value>
</Bonus>
<Prerequ>
<RaceTrait>
<Option>SyntheticLife</Option>
</RaceTrait>
</Prerequ>
</PlanetaryProject>
edit: P.S. I was looking forward to his answer when I heard the question on the stream. I understand the lack of specificity due to assumptions . Unfortunately, this close to release, I suspect synthetic races will still have issues at 1.0, another issue I recall being brought up is that the new assembly improvement is dependent on using the Yor tech tree when using custom races with the Synthetic Life trait. It should be tied only to the trait, not to the tech tree. Especially if the Yor tech boni do not apply to the Assembly improvement.