Based on all the circumstances, I think it's reasonable to assume the risk of involvement of forced labour is higher with Temu than with Nike or Adidas. This isn't a claim that the latter represent no risk, it's a claim they represent less risk than Temu.
Temu's business model involves shipments that are exempt (the so-called de minimis exception) from inspections, duties and data provision to Customs and Border Protection (CBP), to which higher value shipments would be subject (i.e. shipments over $800 - Nike and Adidas shipments are well in excess of $800).
According to the committee's interim report (Select Committee Releases Interim Findings from Shein & Temu Forced Labor Investigation), Temu didn't claim to have "any compliance or auditing system to independently verify that the tens of thousands of sellers who list on Temu are not selling products produced with Uyghur forced labor."
The likes of Nike and Adidas claim to conduct inspections (announced and unannounced) of their supply chains, they claim to have supplier contracts that prohibit sourcing anything (yarns, textiles, goods) from Xinjiang, they report their compliance issues in their annual reports, etc etc, and they likely have evidence for these claims. Again, none of this is to claim they are perfect, it is a claim they are (a) claiming to care (again, Temu doesn't) and (b) they can provide some evidence of making some effort (Temu can't/won't).
Temu itself admitted it "does not expressly prohibit third-party sellers from selling products based on their origin in the Xinjiang Autonomous Region". Temu does not prohibit the sale of products that explicitly advertise their Xinjiang origins. Temu's website listed at least one product purported to be made from "Xinjiang Cotton". In US law - the Uyghur Forced Labor Prevention Act or UFLPA - there is a rebuttable presumption that such goods are made by forced labour, i.e. the importer must prove they were not made by forced labour.
As Temu is not the importer of record with respect to goods shipped to the United States, the laws against importing goods made with forced labour do not apply to it, they apply to the individual person (who isn't having their import inspected, because it's de minimis, or doing other compliance given they are just an ordinary member of the public, not a company). As Nike and Adidas are the importers of record for their goods, they are subject to the laws pertaining to the products of forced labour.
So the one hand you've got a business that isn't even claiming to care to prevent forced labour, it's not subject to US law pertaining to the products of forced labour, its shipments are exempt from scrutiny by CBP, it does sell products sourced from Xinjiang.
On the other hand you've got a business that is at least claiming to care (and to some extent can back this up), it's subject to US law (and European and UK law, I'll add) pertaining to the products of forced labour, its shipments are subject to scrutiny by CBP, and at least appears to make an effort to avoid using anything sourced from Xinjiang.
Someone has commented that "This answer is based exclusively on faith and racism."
Wrong. My answer is not racist, it is business-ist.
I don't assume USA=good and China=bad. I haven't written or indicated anything of the sort here.
I assume that (big) businesses anywhere will often do wrong - or don't care if wrong is done - if they can profit. I assume they are often amoral profit-seekers.
A shocking assumption, I know, but there is plenty of precedent everywhere. As a consequence, many if not all legal jurisdictions have developed myriad regulations on business.
Those regulations create different (dis)incentives depending on jurisdiction and business model.
Nike and Temu are exposed to different (dis)incentives.