I would recommend Odorlos or Happy Camper toilet treatments. However, as I have found, you should be aware that porta potty toilets unlike a regular rv toilet with black tank (and also some cassette toilets) do not have a vent for their self containted black tank to allow gases to
escape. This means gases can build up regardless of the treatment used, particularly in hot weather. So you may at times need to use caution when opening the valve as those built up gases can rush out. It is recommend to do so with the lid down first to release any gases built up, then use, then flush. Use same caution when "servicing" the unit.
Scamper Jim here has a great mod where he added a vent to his porta potty for this same reason and I am about to do the same to mine. Dometic actually makes a retrofit vent/pump out connection that can be added to my Dometic model to convert it to a permanent installation, or you can buy a replacement black tank that already has it installed. This is common in the boating world from what I have found.
Back to your original question, Odorlos and Happy Camper both work in similar fashions as to how they address the "bad bacteria" that produces the offensive odors. With a vented black tank even if it is a porty potty I believe these are probably 2 of the best products available on the market without the "chemical" smell. YMMV