Hi and welcome to the forum:
You might want to correct your title as you indicated the R5, which is actually a high-end full-frame camera, and that is confusing. First, understand that investing in a great lens will provide you better results than buying a high-end body with cheaper glass. A lens is a much longer investment, as bodies come and go with relative frequency, but a lens can deliver excellent results for decades.
With that in mind, while I absolutely recognize your expectations, and the excellent options my respected colleagues have offered, if you were prepared to add a small amount to your budget, you could get the absolutely fabulous RF14-35f/4 IS USM.
It will perform beautifully on a R50 body, and its image stabilization will be a boon for hand-held videography, something that is lacking on the Sigma units (which are otherwise excellent). It is weather sealed, is built like a tank and, with lens corrections turned on (which is the default normally), it will provide high levels of lens correction, which is often a challenge with ultra-wide lenses. Lens corrections for RAW images are now automatically applied in all 3rd-party post-production software, and there is no focus breathing when you zoom in or out - focus breather is a phenomenon where the view expands or contracts as the lens changes focus but the focal length is supposed to stay constant. Focus breathing can be quite disconcerting for those encountering that phenomenon in videos. The constant f/4 aperture will allow you to maintain that aperture for video work and the wider aperture will help you to shoot in low light, and also use it to separate objects from background clutter. The wider 14mm, short focal range will make significant differences in getting up close and personal to parts of cars. I should note that crop-frame cameras, like your R50 will be at a disadvantage at the wide end for ANY lens (both RF and RF-S) attached to them because of the cropping effect of the sensor.
It has the advantage this if you decide at a later date to move to full-frame, it will work beautifully with them. You can get one from Canon's Refurb store for a reduced price. These are new but over-stock, new but open box, demo, or display units, but 'good as new' and come with a Canon warranty.
Shop Canon Refurbished RF14-35mm F4 L IS USM | Canon U.S.A., Inc.
I have this lens myself and can attest to the high quality of the build and optical performance.
cheers, TREVOR
The mark of good photographer is less what they hold in their hand, it's more what they hold in their head;
"All the variety, all the charm, all the beauty of life is made up of light and shadow", Leo Tolstoy;
"Skill in photography is acquired by practice and not by purchase" Percy W. Harris
