Can keywords in the URL path be separated by commas for Google?

Browser will encode input, according to the character-set used in your page.

I personally avoid , in url structure, because of encoding. It's %2C.

So your url would be like /url=keyword1%2Ckeyword2.

Commas are allowed in the filename part of a URL, but are reserved characters in the domain.

* From the URI RFC:

2.2. Reserved Characters

Many URI include components consisting of or delimited by, certain special characters. These characters are called "reserved", since their usage within the URI component is limited to their reserved purpose. If the data for a URI component would conflict with the reserved purpose, then the conflicting data must be escaped before forming the URI.

 reserved    = ";" | "/" | "?" | ":" | "@" | "&" | "=" | "+" |
                "$" | ","

The "reserved" syntax class above refers to those characters that are allowed within a URI, but which may not be allowed within a particular component of the generic URI syntax

While it's definitely possible to use commas in URLs, it's not a widely used practice, nor is it recommended.

Further reading: https://www.searchenginenews.com/sample/content/are-you-using-commas-in-your-urls-heres-what-you-need-to-know

Commas are not typically used in URLs and are not recommended. You should stick to using either underscores or hyphens/dashes. That being said, Google recommends hyphens/dashes, so I would go with that: https://support.google.com/webmasters/answer/76329?hl=en