Again, what are the advantages of a minority investment for Qatar?
There are a number of potential advantages.
They don't have to run afoul of any issues with being majority owners of two clubs in the CL or deal with potential public relations blowback from that.
Under the right terms, they can still associate themselves with a major English football institution, do various things to get that club and Qatar associated as brands, and therefore integrate themselves further into UK society, culture, and influence.
The cost is a lot lower than outright buying a big club. Hypothetically, maybe they think they will get like 75% of the sportswashing benefit for 30% of the cost or something like that.