Are solar terms such as beginning of spring on the same day every year?

Not on the same day, a day or two at most. Gregorian calendar and lunar calendar are attributes, just like people divide men and women. The Gregorian calendar takes the tropic year as the average age, and the lunar calendar takes the moon (lunar calendar) as the average month length. The lunar calendar is actually a combination of yin and yang, and the 24 solar terms are part of the Gregorian calendar, which is a kind of Gregorian calendar, so the Gregorian calendar date is relatively fixed.