Does rz and sz have the same pronounciation?

I find them really Identical like they have the same "shh" sound. Przepraszam is the perfect word that describes my concern.

Depends on words. RZ after voiceless P sounds like SHH indeed but when it is on its own like in RZESZÓW, then it sounds like ZHH. It is a simple devoicing change which often happens. Also in English. :)

Good example.

The Polish letters RZ/Ż are pronounced like Polish SZ (which is somewhat equivalent to the 1st English "SH" in the word "Shush"), plus Polish SZ is pronounced like Polish RZ/Ż (which is somewhat equivalent to the French "J" in the word "Bonjour") under these spelling circumstances:

- Polish RZ/Ż is pronounced like Polish SZ when immediately followed by these individual or clustered "Voiceless" Polish consonants:
C (including Polish CH and CZ), Ć/Ci, F, H, K, P, S (including Polish SZ), Ś/Si, and T.
(There are no changes from original spellings, even though there's a change in pronunciation a.k.a. "Devoicing")

- Polish RZ (but not Polish Ż) is also "Devoiced" as Polish SZ when immediately after individual or clustered "Voiceless" Polish consonants:
C (including Polish CH and CZ), Ć, F, H, K, P, S (including Polish SZ), Ś, and T.

(Note: Polish W is "devoiced" as Polish F also when immediately before or after the above "Voiceless" Polish consonants)

- Polish SZ is pronounced like Polish RZ/Ż when immediately followed by these individual or clustered "Voiced" Polish consonants:
B, D (including Polish DZ, DŹ/Dzi, and DRZ/DŻ), G, Z, Ź/Zi, and Ż.
(There are no changes from original spellings, even thought there's a change in pronunciation a.k.a. "Voicing")

- When Polish RZ/Ż is spelt in last-letter position, it is "Devoiced" as Polish SZ, with no changes in original spellings.
(although except when the very next word in sequence begins with a "Voiced" consonant pronunciation in 1st-letter position immediately before 1st vowel, plus if there's no spoken hesitation between those words. Please read below for more information about "Voiced" Polish consonants).

- When Polish SZ is spelt in last-letter position, it is "Voiced" as Polish RZ/Ż if the very next word in sequence begins with a "Voiced" consonant pronunciation in 1st-letter position immediately before 1st vowel, plus if there's no spoken hesitation between those words. There no changes in original spellings.

(Please read below for more information about "Voiced" Polish consonants).

Those "Voiced" pronunciations in 1st-letter position immediately before 1st vowel of word, are these individual or clustered "Voiced" Polish consonants:
B, D (including Polish DZ, DŹ/Dzi, and DRZ/DŻ), G, RZ/Ż, W, Z, and Ź/Zi.

(Those also includes if those individual or clustered "Voiced" Polish consonants in 1st-letter position are immediately followed by these Polish consonants J, L, Ł, M, N/Ń, and Polish "Rolled R"...and then immediately followed by 1st vowel of word).

(Note: In some parts of Poland, "Voiceless"/"Voiced" Polish consonants spelt in last-letter positions are also pronounced as "Voiced" if very next word in sequence begins with a vowel, plus if there's no spoken hesitation between those words. Also in some or other parts of Poland, "Voiceless"/"Voiced" Polish consonants in last-letter positions are also "Voiced" if the very next word in sequence begins with Polish consonants J, L, Ł, M, N/Ni, and Polish "Rolled R", plus also if there's no spoken hesitation between words. In all the above cases, there's no changes from original spellings).

"W Szczezbrzynie chrzaszcz brzmi w tcicinie" is still excellent practice for foreigners trying to learn Polish pronunciation with humor.

Grzegorz Brzęczyszczykiewicz, Polisch citizen, speech therapist, born in Chrząszczyżewoszyce, county Łękołody, died in Mszczonowieścice, district Grzmiszczosławice, county Trzcinogrzechotnikowo.😂

Ya got me that time, Alien!