Same issue!
Boost For Lemmy
Community of the Android app Boost for Lemmy
Yeah it's been a long-standing issue. Considering that Lemmy's development is happening faster than Boost's, I'm considering finding a new app.
I kinda feel you on that. I used boost on reddit, and when it was announced for lemmy, I bought it immediately. I haven't regret buying the app. I felt bad for the developer community on reddit, and I wanted to be supportive.
I do get that with a considerably smaller userbase development can't be at the same pace... But that doesn't mean that I wouldn't appreciate something as basic as "display all media that the host device can display natively" being implemented.
OP, not only do I have the same issue, I seem to have had the same, or similar, phones as you. I was on a OnePlus 7t Pro and now I'm using a Moto G Stylus 5G. I've had this issue with Boost on both phones. Viewing the post in a browser shows the media just fine. I can download the image or video through Boost with no issue. I just can't see the media in Boost itself.
Maybe it's a dns issue? Try changing your dns to 1.1.1.1
I don't think it's DNS. I mean I can access the files, they just wont show in boost, which leads me to believe that it's an app issue.
Besides on my previous phone I used quad9 over TLS, and on my current phone I use whatever I get through DHCP. So even if I'm using quad9 as the primary DNS on my home WLAN's DHCP (which I probably am), I still use my ISP's DNS while on 5G, and the problem persists there as well.
It's definitely not DNS. I have the same issue as OP and what I've found is that not only can I hit the download button in Boost to download the file and open it locally with no issues, but I can open the post in my phone's browser and it will display the media just fine there. I suspect it's something to do with the particular format the media is saved in. I've seen this with both video and pictures.
For me the small preview always starts playing but the maximised version sometimes never shows.