Quick take
Fine membrane filtration and reverse osmosis are the strongest household categories on first principles, but exact model testing is preferable because particle sizes vary widely.
Best broad-treatment category: reverse osmosis
RO membranes are much finer than typical microplastic particle sizes and can also reduce many dissolved contaminants.
Ultrafiltration can be relevant
UF membranes physically retain small particles and can be effective for particulate concerns without RO reject water, depending on pore size and integrity.
Do not use TDS as a microplastic test
TDS meters estimate dissolved ionic material. Microplastics are particulate and may not meaningfully change a TDS reading.
Prefer actual finished-system testing
Marketing claims about membrane pore size are useful context, but model-level lab data gives stronger evidence that the assembled product performs as claimed.