Reproducted in 1.19.4, 1.20.2 and 1.20.3-rc1.
In the advancements and scores of entity selectors (target selectors), commas can be omitted.

*How to reproduce*
The following commands can parse normally:

/execute if entity @s[advancements={example=true example2={x1=true x2=false}}]

/execute if entity @s[scores={a=1 b=2 c=3}]

/execute if entity @s[scores={a=1b=2c=3}]