does tretinoin really become useless under sun exposure?

i had to buy sunscreen when i read online, on vogue and reddit, that "retinoids become completely useless under sun exposure". the thing is, sunscreen is really expensive here, compared to retinoids, and i really, really, really do not want to reapply it every two hours- that sounds both hellish and very very expensive. so my question was: what does it truly mean? does it erase any/all work done by the retinoid if sun light gets you? making the application utterly unfruitful? what if i only apply at evening with no sun exposure, will it get useless/be for nothing the next day? what if i just use one application of sunscreen? what percentage of retinoid in your screen breaks down? for context, where i live, except summer, the UV index is usually very moderate or low, so at max it is around 3-5 during non-summer days and for a good amount of the day stays so low that it would be absurd to apply sunscreen. so around 4 hours of moderate-high UV index so i dont really see why i should wear sunscreen but all these articles by vogue and redditors seem to imply that without sunscreen, that too with reapplication, it is utterly non-beneficial to use retinoids as it is essential