iPhone SE (1st Gen) won't enter recovery mode to reset passcode

Hello!

I have an iPhone SE (1st Gen) Model A1723 that's running on iOS 15.7.9 (according to my Apple ID).

I'm having a lot of issues with trying to reset my passcode. The last time I used this phone was probably around 2 years ago so I have long since forgotten it. I wanted to access the phone so I could remove my AirTag associated with it to give away to a friend. My attempts to follow the instructions here If you forgot your iPhone passcode or your iPhone is disabled - Apple Support failed because instead of my iPhone going into recovery mode to connect to my computer it would instead pull up a Diagnostic Mode. No matter how long I hold the Home button, it always opens Diagnostic Mode instead. I've even tried a holding down multiple combinations of buttons while having both iTunes and Apple Devices app open on my PC but it always goes back to the Diagnostic Mode.

Ultimately, what I want to do is remove my AirTag from my Apple ID, but I don't have another iPhone or iPad (in fact, this iPhone and AirTag are my only Apple devices) to use to remove the AirTag. From what I've researched and seen on this page If an item or device is connected to another Apple Account - Apple Support, the only way to remove an AirTag is using the FindMy app on an iPhone or iPad logged into your Apple ID since the AirTag won't show up under your devices anywhere else. (I've also reset the AirTag following this page How to reset your AirTag - Apple Support and while I was able to successfully reset it, it won't allow me to add it to a new Apple ID since it's still paired to my old one).

I really don't want to have to pay to have this fixed or to see someone at an Apple store if it's a simple fix. (Also, I'm living in Japan right now and my Japanese is not equipped with technical language). I'm wondering if perhaps because my iOS is out of date and the iTunes and Apple Devices are updated, it's causing issues with getting the phone into recover mode. (My device is also on Airplane mode if that affects anything).

Would love some possible solutions I can try because I'm kinda desperate here. I really would like to give away this AirTag because my friend really needs one, but we're not trying to buy a new one when a perfectly useable one is available.

Thanks in advance for anyone who's able to offer some help!