Then your options are very limited, especially during the pandemic. Osaka is like Tokyo's uglier, retarded younger brother. The people pride themselves on being "friendly" (as opposed to the "cold" Tokyo folks, whom they hate) but they are truly just stunted, moronic and infinitely less international and cosmopolitan than Tokyo people. Can I assume you're white? If so, the people will gawk and leer at you and possibly try to practice their English with you, but accepting you as a customer (or lay) is an entirely different thing.
The only reliable FS in Osaka, especially for foreigners, is Tobita Shinchi. A search here will result in more than you need to know. It's basically window-shopping in three designated alleys, 20 minutes for 16,000 yen (price might've changed, haven't been there in a while). Process is rushed and to the point: You get the blessing from the mamasan, girl takes you upstairs, pay the girl, you strip, girl cleans your equipment with a towelette, applies condom with mouth, rides you briefly and then you can finish in whatever position works for you in the 10-15 minutes you have left. Buzzer warning sounds, you get the fuck out asap, wave goodbye and you're walking back to Tennoji Station.
Even in the best of times, I would say only half the shops will accept white foreigners, and that's IF they can speak Japanese well enough to satisfy the mama. I'm ethnically Japanese and speak the language well enough so I've never been turned down at any shop. During my years living in Osaka, my British/Aussie friends would hit Tobita as often as their paychecks allowed and were actually welcomed by the majority of the mamas, but they were also quite fluent and decently handsome and that goes a long way. I've heard from a buddy of mine who still lives there that Tobita was operating on a limited basis and most shops have banned foreigners regardless of language ability, but that was a month ago and a lot can change...although probably not in your favor.
If you're set on going to Osaka and want reliable FS, your best bet would be to just try your luck at Tobita. Learn enough Japanese to ask the mamas if they're allowing foreigners and don't set your expectations very high. The only indy on TAG has apparently stopped working for the time being, so unless you want to try your luck and risk a lot of disappointment by prowling around back alleys in Namba/Umeda, there aren't many other reliable options for you. Of course, you could try the traditional method of picking up drunk/desperate women at gaijin bars or clubs. I've had lots of success (if you want to call it "success") with that routine. I've also talked my way into all sorts of abominable acts of depravity and disgust at Chinese massage shops, but again I can speak decent Japanese and with my Japanese face, I suspect they put up with a lot more shit from someone who looks like me. FWIW, just about all of the Chinese massage shops that I've staggered into--be it in Osaka or otherwise--have at some point offered me FS.
And just throwing this out there...in case it's not a deal-breaker for you if the girl you're banging isn't actually a girl, there are a number of new-half shops in Umeda, Namba and Nipponbashi that very enthusiastically welcome foreigners, like Libe and Club Diamond. I've never tried them, but I used to frequent a hotel next to one of these shops and the "girls" would regularly hang around outside smoking cigarettes. From what I saw, it would basically amount to corn-holing a really ugly guy in a wig and skirt, but your options are very limited so when in Rome?
Of course, you could choose the smartest option: Cancel your trip to Osaka and go to Tokyo.