I am trying to use
ps -C chromi*
to see all chromium processes, but no success. How can I use regular expression in here?
How to use "Regular Expression" in ps?
You cannot, ps does not support regular expressions. The argument is parsed literally.
How to use "Regular Expression" in ps?
You can patch procps ps to support it, most probably (with yet another!) additional flag. The patch looks simple, basically another tree traversing parse_* function that uses regex.h instead of strncmp.
I doubt such patch would make it upstream - it's typical to use other tools, most notably pgrep or shell with a pipe and grep, to filter process by command line name. ps has to stay POSIX compatible, and has so many options already.
Note that regular expression is not "globbing". Consult man 7 glob vs man 7 regex. Regular expression chromi* would match chrom or chromiiiii - chrom followed by zero or more i.
Note that unquoted arguments with "trigger" characters undergo filename expansion (ls 'chromi*' vs ls chromi*). This is different than passing the literal argument when there exist files that match the pattern. If the intention is to pass the pattern to the tool, quote the argument to prevent filename expansion.