You want a penetrating sealer made with siloxane/silanes. I like Sika products, use Sikaguard 70 if you can find it here at Home Depot mexico. Not cheap but it is what you want.
They are not acrylics and do not form a seal at the top of the tile. They breathe and penetrate concrete, tile and other porous masonry surfaces without changing the look of the material. Any top coat sealer will degrade in the sun. Read the review at the link here and then begin your search with your tradesman to find the product locally. If you have a failing finish on your tile it has to be stripped to get the porosity back so the penetrating sealer can get in as deep as possible. Just sprinkle water on the surface and if it does not absorb and turn dark you have to strip or wait to seal with a penetrating sealer.
Watch out for waterbased formulas with silicone. I am not a fan yet of these hybrids that have acrylic mixed with some silicone but I think Okon S40 is a good product if you can find it here. I generally prefer oil or solvent based penetrating sealers although there are some waterbase siloxane/silanes that pentrate and perform well. Home depot carries Thompson’s Waterseal Multi-surface but their website and info at Home Depot is lacking information about what it is in it and the reviews by users are horrible. They lowered the VOC’s (volatile organic compounds) probably to meet California standards and made it thicker and stickier and it creates a mess on your concrete/masonry surfaces. Always do a small test patch first.
Go to Services and then Subcontrator Referrals on this website to find several tile refinishers that you can contact. Stay away if they do not recommend a penetration sealer for the exterior.