Alibaba and AliExpress collect VAT on behalf of HMRC on shipments <£135. Have Shein and Temu managed to avoid joining the VAT club?
IMO, collecting duty on cheap tat wouldn't be worth the effort, unless it's calculated at source and not at the border. Calculated at source could yield a worthwhile sum to the UK's coffers because a big slice of the imports will attract 12.5%.