Look into AptX Adaptive USB transmitter dongles (like KB9P), they're often ~$15-20 on AliExpress/Amazon/etc.

In theory you can use those USB transmitter dongles to output AptX Adaptive with any device that has USB. So use USB-C or USB-A adapters/converters if needed. Btw, it seems you have to get the 16-bit version for compatibility with older devices like say TV, otherwise go for the 24-bit version as those are often newer and have bugfixes and so on. They're like the same price, so just get the 24-bit versions of the AptX Adaptive dongles.

For the KB8P and KB9P there's also the Dongle Assistant software, a few people have translated it to English, check the Head-Fi thread linked below.

There's ~$20 AptX Adaptive USB transmitter dongles like the KB9P. It'll go well with AptX Adaptive receivers/devices like Qudelix 5K and FiiO UTWS5. And of course TWS earbuds that have AptX Adaptive.

Here's more (direct) updated info about the AptX Adaptive USB transmitter dongles (KB8P, KB9P, YET-T10P): https://www.reddit.com/r/headphones/comments/zfkxgf/can_i_use_a_bluetooth_transmitter_to_bypass_s22/izcyrvn/ and https://www.reddit.com/r/HeadphoneAdvice/comments/x49xwl/bluetooth_52_aptx_adaptive_latency_with/imune2x/ and https://www.reddit.com/r/HeadphoneAdvice/comments/s54lbx/wireless_closed_backs_for_general_pc_use/imqv9px/

Here's more updated info about the AptX Adaptive USB transmitter dongles (KB8P, KB9P, YET-T10P): https://www.reddit.com/r/headphones/comments/zfkxgf/can_i_use_a_bluetooth_transmitter_to_bypass_s22/izcyrvn/

This thread link talks about the Qudelix 5K, AptX Adaptive dongles, and specifically Apple devices: https://www.reddit.com/r/headphones/comments/zc1znn/qudelix_5k_arent_these_issues_a_big_issue/iyuh35j/

This is the Head-Fi thread for those AptX Adaptive/Lossless dongles and other Bluetooth transmission stuff: https://www.head-fi.org/threads/aptx-adaptive-aptx-lossless-usb-transmitters.961856/page-52

If you want Bluetooth or TWS earbuds for PC/et cetera, here's also more direct info: https://www.reddit.com/r/HeadphoneAdvice/comments/z74tif/wireless_earphones_for_pc_microsoft_teams/iy59w0n/

Hopefully we get QCC5171 TWS earbuds and TWS adapters soon as there's now QCC5171 neckband adapters with AptX Lossless and so on. And like hopefully Bluetooth 5.3 LC3/AptX Lossless/etc. USB transmitter dongles soon too.

Newer Bluetooth 5.3/etc. dongles will come out from Taobao/China, IIRC they're also maybe developing LDAC (maybe LHDC too, it's like an LDAC equivalent (LHDC has an additional low latency version), usually only found on Xiaomi devices) USB transmitter dongles. So that should come out after or like the same time. It depends on how the Qualcomm/etc. chipsets go when they implement/hack it together.

Anyway, for the storage, 128GB and 256GB microSD cards (SDXC/etc.) should be like pretty cheap, less than $50 these days. Latest phones should have OTG cable/etc. stuff already but if you're using older phones for storage, don't forget to get a legit OTG cable or cable that allows proper data transfer.

Like if your phone has no microSD card, you'll have to use external storage or the cloud storage and so on.

I have basically everything in FLAC and then the few other files are 320kbps MP3 files. Or if it's from ASMR (Here's some videos/channels for ASMR triggers: https://www.reddit.com/r/headphones/comments/xqq9kw/can_a_normal_person_hear_binaural_sound_when/iqcayk9/) then it's sadly from Youtube compression already, though back then and even these days some ASMRtists will give away their source or FLAC files for free/cheap on Bandcamp and so on.

So having everything in FLAC is for the peace of mind. If you're storage-constrained, go for 320kbps MP3 or 256 kbps MP3, that's constant bitrate (CBR) not variable bitrate (VBR) btw, but you can also do VBR since some people don't mind. Or ya opus since some people like that format.

Don't worry too much about bitrate loss and so on as everything is still lossy/compressed/etc. even with the new AptX Lossless from Bluetooth 5.3/LC3/etc. that won't be enough for really picky people that like to look at things on paper, lol. Like in practice most people won't be able to notice, especially since they use TWS earbuds/adapters/receivers/etc. outside.

When you're outside, a lot of external noises are competing with the music/sound from the TWS earbuds. Especially since some people don't try to go for that good/perfect fit for that vacuum seal (necessary for bass to be heard properly). And so without that vacuum seal (especially with stem style TWS earbuds, like AirPods, as those have little to no ear tips), there's way less noise reduction/isolation.

With Apple TWS earbuds or Bluetooth devices, those have hardware/software/etc. that make them sound good (through AAC) when paired with iPhones or other Apple devices that have a particular chip, like the new H2 chip or something like that.

So with Android you'll have access to LDAC, LHDC (this is basically only for Xiaomi phones), AptX Adaptive, and now AptX Lossless (few phones have it, like Motorola, ASUS, etc. have like one or two models so far, it's not mainstream yet). Those Bluetooth codecs have better sound quality than AAC in theory (though again Apple does special things though with their proprietary chips if both your TWS earbuds and phones are from Apple) and so ya.

You can do (parametric) EQ with $8 Neutron Music Player or UAPP on Android. If on PC, the free (Peace) Equalizer APO. There are free apps on Android(/Apple) that can also do a good enough job, but most of them have those graphics sliders instead of parametric or just plug the numbers in EQ. EQ can also be used to help with channel or ear imbalances.

Neutron and UAPP are the usual audiophile apps. Some people use the free/etc. options like Wavelet, which also has AutoEQ.

If you like a particular sound, try looking into squig.link graphs for comparisons and so on. You can try using the AutoEQ there to make IEMs/headphones sound like the others, just keep in mind that obviously it's not going to be the exact same sound.

Here's Super* Review using the new AutoEQ feature of his squig.link site: https://www.youtube.com/watch?v=RWzBw3XBn8c&t=332s

Use any EQ list or AutoEQ from squig.link as a base for your preferred taste. So like adjust the treble/bass/etc. areas if the Harman/crinacle/etc. target is still too much for you.

TL;DR: get the $20 KB9P AptX Adaptive USB transmitter dongle, some microSD cards or external/could storage, and then call it a day with any file/audio format you want as in practice most people won't be able to tell the difference when outside/etc.