Hello
thx for reporting
just set PHP to not display Deprecated msg and Notices

manually fixed ... ("just set PHP to not display Deprecated msg and Notices" <- it doesn't help the Responsible programmer if any user hide deprecated msg/notices => nobody realized that the rss-feed isn't php7-ready ...)

a new feedcreator.class.php from <http://feedcreator.org/> don't resolve the problem. Forget it!

to fixed the deprecated Message:
open include/feedcreator.class.php

Find the line ( ... FeedHtmlField has a deprecated constructor in /****/include/feedcreator.class.php on line 275 )
275 = class FeedHtmlField {
Finde the function with same name (291: function FeedHtmlField($parFieldContent) { )
Replace ["function NAME" (function FeedHtmlField) by public function __construct
=> don't change the content of ( ) - only replace function NAME !
=> do this with every deprecated line ...
=> Save

After this: make a copy of this file! (in the next Piwig-Version no fix? reactivate your copy)

WuppiGER wrote:

not fixed in 2.9 :(

I just open a bug in piwigo tracker about this issue.
[Github] Piwigo issue #678