Start with the hem, not the boot
Stand in your jeans with the shoes you actually plan to wear. A hem that lands cleanly at the top of the boot gives an uninterrupted line; one that bunches heavily may need a cuff or a different pair. Leave enough ease to sit and walk.
Check the combination from the side as well as the front. The question is not whether jeans must cover boots, but whether the break looks intentional and stays comfortable through a full day.
Straight jeans: the easy middle ground
A straight leg can skim over a slim ankle boot or stop just above it. Keep the gap small when warmth matters, using a sock in a related color if skin would otherwise show. A pointed toe elongates; a rounded toe reads more casual.
For a relaxed outfit, add a plain knit and a jacket whose hem finishes above the widest part of the jeans. For a sharper version, use a tucked shirt and a belt that repeats the boot color.
Wide and cropped jeans need different proportions
With wide jeans, choose a boot with enough presence that its toe does not disappear under the hem. The fabric can fall over the shaft, but it should not drag on wet pavement. A shorter top or defined waist restores the outfit's proportions.
Cropped jeans deliberately expose the boot. A close-fitting ankle shaft usually creates a cleaner transition than a very loose one. If the crop is high, a tall sock can turn the visible space into a considered layer.
Choose for the day you have
Rain, stairs and walking distance matter more than a rule about matching denim cuts. Try the outfit on with outerwear, walk a few steps and check whether the hem catches or the boot rubs. The most wearable combination is the one you can forget about once you leave home.