Don't know if this would be of any interest but I came across a lesser-known and (I think) fairly new streaming service called DistroTV, their main page is at https://www.distro.tv/live/ and they seem to have some channels not found on some of the other services. The channel list and EPG are at https://github.com/DeltaSr95/DistroTV but you will probably want to use the "raw" version of the m3u list at https://raw.githubusercontent.com/DeltaSr95/DistroTV/master/distrotv.m3u (otherwise it is encapsulated in html which won't work in player software). This is not a recommendation or anything, I just found out about it while looking at a page at https://thefrugalstreamer.blogspot.com/p/free2viewtvpage1.html which may also contain links to some other interesting streams but for some reason I have a real problem with the layout or the font or something about that page, I can't put my finger on it but there is something about it that makes it hard to read, for me anyway. They also have a big master list of streaming channels but it's not nearly as large as the other one. Anyway, for those who think you just can never have enough streaming channels, there's a few more for you.
EDIT: I tried adding DistroTV in Cabernet and everything appeared to work until I got to the point of trying to scan the channels into Tvheaded. Tvheadend finds the muxes with no problem, but then when it start scanning them only about one quarter of the channels will scan in. The problem is that the links provided by Cabernet to Tvheadend don't seem to work; if I copy the link of one that won't play from the mux configuration and put it in VLC it still won't play, but if I use the original .m3u file from github then most of the channels do play. As a random example of one that won't play through Cabernet but will play directly, try channel 62 (MotoAmerica). My settings in Cabernet for the instance are as follows:
[m3u_distrotv]
label = M3U DistroTV
channel-m3u_file = https://raw.githubusercontent.com/DeltaSr95/DistroTV/master/distrotv.m3u
epg-suffix = D
enabled = True
channel-import_groups = True
player-enable_pts_filter = True
player-enable_pts_resync = False
epg-xmltv_file = https://github.com/DeltaSr95/DistroTV/blob/master/distrotv.xml.gz?raw=true
All the rest are the defaults for a m3u instance. I tried various combinations of player-enable_pts_filter and player-enable_pts_resync but nothing seemed to make any difference. Don't know what is so different about these streams, except that I suspect from watching VLC that some of the links in the original m3u file might go to intermediate redirects before getting to the actual stream link.
EDIT 2: I think that is precisely the problem, there are too many layers of m3u8 files. If you download the file from https://raw.githubusercontent.com/DeltaSr95/DistroTV/master/distrotv.m3u and find the link for MotoAmerica it shows this:
#EXTINF:-1 tvg-id="dtv_EPGMotoAmerica TV" tvg-name="MotoAmerica" tvg-logo="https://a.jsrdn.com/hls/22964/motoamerica-tv/logo_20210929_171411_68.png" group-title="Sports",MotoAmerica
https://dai.google.com/linear/hls/event/HCkYA2wESb6G9YpN6SyD0A/master.m3u8
A link to another m3u8 file! And if you download that, it shows this:
#EXTM3U
#EXT-X-VERSION:3
#EXT-X-STREAM-INF:BANDWIDTH=2000000,RESOLUTION=960x540,FRAME-RATE=30,CODECS="avc1.64001e, mp4a.40.2"
https://dai.google.com/linear/hls/pa/event/HCkYA2wESb6G9YpN6SyD0A/stream/13549f79-779b-4cc4-afe6-652acd882282:TUL/variant/a0369453fc25b34d3a9469a225195a05/bandwidth/2000000.m3u8
#EXT-X-STREAM-INF:BANDWIDTH=750000,RESOLUTION=640x360,FRAME-RATE=30,CODECS="avc1.64001e, mp4a.40.2"
https://dai.google.com/linear/hls/pa/event/HCkYA2wESb6G9YpN6SyD0A/stream/13549f79-779b-4cc4-afe6-652acd882282:TUL/variant/6d56b2f489a0dfe74cd39c91ac1d8330/bandwidth/750000.m3u8
#EXT-X-STREAM-INF:BANDWIDTH=1000000,RESOLUTION=640x360,FRAME-RATE=30,CODECS="avc1.64001e, mp4a.40.2"
https://dai.google.com/linear/hls/pa/event/HCkYA2wESb6G9YpN6SyD0A/stream/13549f79-779b-4cc4-afe6-652acd882282:TUL/variant/f618d6d0e85b5083fcbb2402a52daa68/bandwidth/1000000.m3u8
#EXT-X-STREAM-INF:BANDWIDTH=3000000,RESOLUTION=1280x720,FRAME-RATE=30,CODECS="avc1.64001e, mp4a.40.2"
https://dai.google.com/linear/hls/pa/event/HCkYA2wESb6G9YpN6SyD0A/stream/13549f79-779b-4cc4-afe6-652acd882282:TUL/variant/a856a3d01aca5ee0a5ad0d159acc7b78/bandwidth/3000000.m3u8
#EXT-X-STREAM-INF:BANDWIDTH=5000000,RESOLUTION=1280x720,FRAME-RATE=30,CODECS="avc1.64001e, mp4a.40.2"
https://dai.google.com/linear/hls/pa/event/HCkYA2wESb6G9YpN6SyD0A/stream/13549f79-779b-4cc4-afe6-652acd882282:TUL/variant/f452aa50f451ccd791ac4d48f3c5bc26/bandwidth/5000000.m3u8
Still more m3u8 links! Naturally we want the highest resolution, so try downloading that... I won't post it here because it is a little long, but only at this point do we finally get to a list of streams. But if I put that link into VLC, it will not play. If you put the master m3u list into VLC and select MotoAmerica, and display media information, the link it displays is https://dai.google.com/linear/hls/event/HCkYA2wESb6G9YpN6SyD0A/master.m3u8 which youcan supply directly to VLC (and it actually starts playing a lower resolution for a couple of seconds, then switches up to 720p). It is not that I have any interest in this particular channel, many of the channels on DistroTV have the same issue. I just thought you might want to know that for whatever reason Cabernet is having some trouble with this provider, and my suspicion it that the data it wants to see is buried a layer or two too deep.