Mikvah and John the Baptizer

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Mikvah (מִקְוֶה) is a bath used for the purpose of ritual immersion in Judaism to achieve ritual purity.

Tevilah (טְבִילָה) is a full body immersion in a mikveh

Wiki:

In October 2020, a 2,000-year-old mikveh was found near Hannaton in northern Israel.[11]
A mikveh must, according to the classical regulations, contain enough water to cover the entire body of an average-sized person; based on a mikveh with the dimensions of 3 cubits deep, 1 cubit wide, and 1 cubit long, the necessary volume of water was estimated as being 40 seah of water.[14][15]
Cases where the Torah or rabbinic law requires full immersion include:

• one who wishes to become pure after Keri[23] — normal emissions of semen, whether from sexual activity, or from nocturnal emission. Bathing in a mikveh due to Keri is required by the Torah in order that one should be allowed to eat terumah or a sacrifice; Ezra instituted that one should also do so in order to be allowed to recite words of Torah.[24] The latter case is known as tevilath Ezra ("the immersion of Ezra"). In modern times it is no longer considered obligatory, but some perform it as a custom.
• one who wishes to become pure after Zav/Zavah (abnormal discharges of body fluids) or niddah (menstruation), or one who has come into contact with such people or their clothes or articles;[25][26][27] In particular, a married woman must immerse in order to resume marital relations with her husband.

Mikvah was practised at the time of John the Baptizer. However, John did not perform baptism for ritualistic cleansing. Mark 1:

4 And so John the Baptist appeared in the wilderness, preaching a baptism of repentance for the forgiveness of sins.